Nutrient deficiency cause morphological and phenotypic responses in Wheat

8/10/2019 Nutrient deficiency cause morphological and phenotypic responses in Wheat

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Introduction:

Wheat is the most productive and important crop with over 600 million tonnes of

wheat harvested every year, mainly for human consumption and livestock feeding (1).

Further improvement in wheat yield is require to meet the current and impending

challenges (2). Fostering wheat plant can be accomplished by providing adequate

amount of nutrient and water. In order to have a better understanding of the importance

of nutrients, one must recognize the consequences of depriving such nutrient. The

following report provides a background information on the role of macro- and

micronutrients. Also, this report further discuss an experiment conducted to witness the

effect of depriving wheat of certain nutrients. Lastly, this paper addresses the

physiological, morphological, and phenotypic changes for each deficiencies.

Nitrogen Function and Deficiency

Nitrogen is a macronutrient thats vital in promoting plants growth, delaying

maturity, and enhancing the greenness of plants foliage (3). Not to mention, nitrogen

greatly influence the dry weights of the shoot and root of a plant, leaf stomatal

conductance, transpiration rate, photosynthetic rate, and absorbance rate of

micronutrients (e.g. zinc, manganese and copper) (30).

Evidence demonstrates that some symptoms of nitrogen deficiency in wheat

includes delay in growth and chlorosis in wheat plant (4). Further studies also indicated

that the rate of senescence increased during nitrogen deficiency (5). Not to mention, the

rate of root elongation decreased which enable to access nitrogen resource from the

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ground. With this being said, one can hypothesis that stem height would decreases and

the fibrous root length decreases. Also, one would observe chlorosis disorder and

withering of the leave.

Potassium Function and Deficiency

Potassium act as cofactor in many enzyme, and used establishing turgor

pressure and maintain cell electroneutrality(3).

In general, plant that endure potassium deficiency showed signs of marginal

chlorosis which develop into necrosis at the tip of the leave (3). Furthermore, studies

are inconsistent with the effect of Potassium on root development. Ashley, Grant, and

Grabov (2005) showed that Potassium-deficiency Zea mays underwent morphological

changes such as triggering root development (31). On the other hand, Drew (1975)

demonstrated that barley plant developed poor lateral root during potassium deprivation

(14). Therefore, no hypothesis can be synthesis about the effect of depriving Potassium

on plant. One can hypothesis that the stem height would decrease due to the decrease

in both the stomatal conductance and photosynthetic rate which resulting in limiting

growth.

Phosphorus Function and Deficiency

Phosphorus is essential to provide energy in the form of ATP to drive

biochemical process such as photosynthesis (33) and is the one of the major

components in genetic information (DNA and RNA). It is not obvious if a plant is

experiencing phosphorus deficiency or some other condition. Therefore, diagnosing a

plant based on general appearance is difficult. When there is a low level of phosphorus,

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the plant usually experience morphological change such as an increased in the root

surface, which enable the plant to gain better access to phosphorus in the soil. Not to

mention, primary root is reduced and the length and density of root hair increases.

Furthermore, the elongation rate of axile and density of root cease to change during

phosphorus deprivation in maize however, new axile root emerges (34). Furthermore,

phosphorus-deficient plant is characterized by their dark green coloration with

reddish-purple leaf tips and margin (34). In addition, the leaf area, leaf elongation rate,

and grain yield are reduced along with delay in leaf and flowering development (33).

Overall, one can hypothesis that the number and size of root would increase.

Sulfur Function and Deficiency

Sulfur is an essential element to synthesis amino, protein, vitamins, and

coenzymes (35). In addition, sulfur is require for ferredoxins to synthesize chlorophyll

(35). Usually, there is an increase in yield, size, and weight when a grain are exposed to

excessive amount of sulfur. General, sulfur deficiency is characterized by chlorosis,

stunt growth, and anthocyanin accumulation (3). Symptoms of sulfur deficiency

including interveinal chlorosis and yellowing leaves, appear in young corn plant (3).

Moreover, sulfur deficiency induces genetic changes cause an improvement in sulfate

uptake, reduction capacity, enhancement of sulphate remobilization from the vacuole

(36).

Calcium Function and Deficiency

Calcium is important for cell wall elasticity and expansion, mitotic spindle during

cell division, and implicated as a second messenger for plant response (3). It is

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responsible for growth at the tip of the plant . Not to mention, calcium assist in the

development of root hair and starch transport (37). Usually, young plant with calcium

deficiency exhibit deformed leaves. In addition, plant grow short and stubby roots when

deprived of calcium.

Magnesium Function and Deficiency

Magnesium plays a role phosphate transfer and constitute chlorophyll molecule. When

a plant is magnesium deficient, the veins become dark green with yellow areas in the

middle of the vein in a phenomenon called interveinal chlorosis. Symptom also include

premature leaf abscission. Therefore, one can hypothesise that the stem height would

be reduced and show chlorosis.

Limited amount of researches were conducted on the impact of depriving wheat

of macro- and micronutrient. With this in mind, a first-hand approach was undertaken to

determine the characterization of the stem height, fibrous root length, adventitious roots,

and weight when starving wheat plant of essential nutrients. Overall, one can

hypothesis that each nutrient will causes various of unique changes on the

morphological and phenotypic structure of the wheat plant.

Experimental Procedures:

This study was performed in a 6 weeks time span in which wheat seedlings were

deprived of certain nutrients. The wheat plant received nutrient via nutrient-enhanced

water. The following treatments were established: a positive control (received all

essential nutrients) , nitrogen-deficiency, potassium-deficiency , phosphorus-deficiency,

sulfur-deficiency, calcium-deficiency, magnesium-deficiency, and

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micronutrient-deficiency. Prior to performing the experiment, the seeds were allowed to

pre-germinate for two days in which the pre-germinated seeds watered and placed in

the dark. Next, three to five pre-germinated wheat seeds were grown in the same pot for

each treatment. Important to mention, the soil pot was 1:1:1 ratio consisting of sand,

perlite, and vermiculite. Table 1 demonstrate the concentration of nutrient given to

individual plants.

Table 1. The type of nutrient deficiency with the corresponding amount of

chemical compounds diluted in 1000 mL solution.

Solution 10 mL 10 mL 10mL 10 mL 2 mL 10 mL

Control Ca(NO3)2 KNO3 KH2PO4 MgSO4 Fe-EDTA 0.5 M Micronutrien

Nitrogen CaCl2 KCl KH2PO4 MgSO4 Fe-EDTA 0.5 M Micronutrien

Potassium Ca(NO3)2 (5mL) KNO3 NaH2PO4 MgSO4 Fe-EDTA 0.5 M Micronutrien

Phosphorus Ca(NO3)2 KNO3 (2mL) KCl MgSO4 Fe-EDTA 0.5 M Micronutrien

Sulfur Ca(NO3)2 KNO3 KH2PO4 MgSO4 Fe-EDTA 0.5 M Micronutrien

Calcium NaNO3 KNO3 KH2PO4 MgSO4 Fe-EDTA 0.5 M Micronutrien

Magnesium Ca(NO3)2 KNO3 KH2PO4 Fe-EDTA 0.5 M Micronutrien

Micronutrient Ca(NO3)2 KNO3 KH2PO4 MgSO4 Fe-EDTA

Furthermore, each plant were grown in a semi-hydroponic environment and

placed under the same greenhouse conditions (e.g. same humidity, temperature, Etc).

After the 6 weeks, the stem height, root length, number of root, and general appearance

of the plant were determined. The height and length was measured using a ruler, while

the weight was measured with a balancing scale.

Each deficiency type was compared to the normal (control) growing wheat plant to

determine if the plant increased or decreased in mean stem height, root length, and

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number of roots relative to the control. Also, the physiological and morphological

mechanism occurred during nutrient deprivation will be discuss.

Results:

In the control pot, no defect was detected (Fig. 1).

(a) (b)

Figure 1. Control. The entire plant (a &b) after 6 weeks.

However, the nitrogen deficiency wheat plant showed delayed in maturity when

comparing to other nutrient deficient individuals (Fig. 2) . In addition, The entire leaf

have developed chlorosis (abnormally yellow color in plant tissue) and exhibit a

reduction in stem height (in comparison with the control plants).

(a) (b) (c)

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Figure 2. Nitrogen Deficient. The following figures show the entire plant (a) along with a

close-up of the stem (b &c) after 6 weeks of being deprived of nitrogen.

Furthermore, the potassium deficient wheat plant exhibited a yellow-brown necrosis at

the tip of the leaves along with marginal chlorosis (Fig. 3) . In addition, the plant did not

produced primary roots, but generated many similar-size lateral roots.

(a) (b)

Figure 3. Potassium Deficient. The stem (a) and root (b) of the potassium-deficient wheat

plant after 6 weeks.

The phosphorus deficient wheat showed chlorosis defect at the tip of the leaves, while the

rest of the plant did not exhibit any further change (Fig. 4).

(a) (b)

Figure 4. Phosphorus-Deficient.The phenotypical changes which occurred on the stem (a)

and root (b) of wheat after 6 weeks without phosphorus.

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The sulfur deficient plant exhibit stunt stem growth and increased in root elongation (Fig. 5).

Not to mention, some leaves of the plant experienced senescence (no longer able to divide

but metabolically active) from the tip of the leaf near the base of the plant.

(a) (b)

Figure 5.Sulfur deficiency. The stem (a) and the root (b) of the sulfur-deficient wheat plant.

Depriving calcium caused the plant to exhibit chlorosis on the margin and tip of the stem (Fig.

6). Such abnormity appeared in the early stage of development. In addition, the stems of the

plant were poorly developed, which caused the stem to tilt at an angle instead of growing

vertically.

(a) (b) (c)

Figure 6. Calcium Deficiency. The phenotypic and morphological changes to the stem (a),

node (b), and root (c) of wheat plant after week 6 without calcium.

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In the magnesium deficiency wheat, there were about 5 seeds grown in the pot and only one

individual plant developed (Fig. 7). In addition, the tip and margin of the stem exhibit chlorosis.

(a) (b)

Figure 7. Magnesium Deficient. The entire plant (a) and the root (b) of wheat plant after week

6.

In the calcium deficient wheat, no visible defect was detected during the plant growth and

development (Fig. 8).

(a) (b)

Figure 8. Micronutrient Deficient. The entire plant (a) and the root of the

micronutrient-deficient wheat after week 6.

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After the 6-weeks time span, the nitrogen-deficient plant possessed the lowest

mean stem height among all treatments, while the potassium-deficient the greatest stem

height (Fig. 10). Furthermore, the potassium possessed the shortest fibrous root, while

the magnesium produced the longest fibrous root. Lastly, micronutrient possessed the

highest weight, while nitrogen possessed the lowest weight. Overall, the K-deficiency

wheat plant endure the greatest morphological changes in this experiment.

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Figure 10. The mean stem height (in cm), fibrous root length, and weight for each type ofdeficiencies after 6 week.

Discussion:

The purpose of this investigation was to determine if certain nutrient deficiency induces

unique morphological and phenotypical changes to the stem and root system. The

following discussion given an overall of the result of the investigation and provide further

evidence to the cause of such changes.

Effect of Nitrogen Deficiency

N-deficient plant demonstrated sign of chlorosis and exhibited senescence.

Evidences confirm that developed wheat plant would suffer from such discoloration

(4,5). This is due to the breakdown in chlorophyll production, causing chlorosis

symptoms to first merge from the tip, then extending downward to the leaf (5). Further

studies indicated that N deficiency triggers a reduction RuBP regeneration and increase

the activation of RuBPCO activity, which overall restrict photosynthesis and further

contribute to chlorosis in the leaves (6). In addition, it was reported that young winter

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wheat plant can also exhibit purple colored leaves due to expression of gene controlling

coleoptiles (4).

Furthermore, the result was consistent with previous studies in which N-deficient

increased the rate of leaf senescence (5). Studies indicated that senescence process

mainly occurred when the leaf reaches its maximum size, in which there is a decline in

the photosynthesis-associated protein and degradation of chloroplast enzyme (7).

Moreover, N-deficient plant demonstrated reduction in fibrous root. This result is

not consistent with other studies (8, 9). Teplova, Veselov, and Kudoyarova (1998)

demonstrated that N-deficiency promoted root elongation and shoot retard in wheat

plant (8). One can postulate that the root elongation enable plant to gain better access

to nitrogen in the soil during N deprivation.

Effect of Potassium Deficiency

Potassium plays a vital role in rate of stomatal conductance, in which K+flux into

and out of the stomatal guard cells. This fluctuation of K+ affects the osmotic potential

within the cell, which determine if the stomatal guard cells open or close. During

potassium deficiency, the stomatal conductance rate decreases, which decreases

photosynthetic process (10). This decrement in the rate of photosynthesis can be seen

by the chlorosis in the stem of wheat plant (11, 5). In this experiment, K deficient leaves

exhibited chlorosis at the lateral and interveinal side of the stem.

Moreover, the stem height was slightly above the control group. This is not

consistent with the result of other studies with other species of plant. For instance,

Masakaa, Mugutia, & Chivandib (2008) underlined that K deficient tobacco plants

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showed 86% reduction in comparison to the control, which received a complete nutrient

solution (12).

In addition, K-deficient plant contained more lateral root than primary roots. Not

to mention, the K-deficient plant roots possess the shortest fibrous root than any other

nutrient-deficient plant. Studies showed similar morphological response with barley and

Arabidopsis (13, 14). During K deprivation, a cascade of cellular activities occur. First,

there is an increased of genes for ethylene production, in which ethylene inhibits root

growth. Secondly, Hak5,AtKC1, and KEA5 genes are up-regulated to encode for K+

transport proteins in order to enhance K+ ion uptake into the root cell. Lastly, reactive

oxygen species (ROS), such as H2O2, increases in certain region of the plant, in which

ROS actively performed K+ uptake and translocation (15). Overall, the plant would

exhibit reduction in root size and undergo genetic and physiological changes during

K-deprivation.

Effect of Phosphorus Deficiency

In comparison to the control, P-deficient plant experienced reduction of stem

height and weight, yet the fibrous root length increased. Results were consistent with

report (5). Reduction in stem height can be explained by the fact that P deficiency limits

cell division at the shoot apical meristem and, thus, inhibiting newly developed leaves

(16).

In addition, Sarker, Karmoker, and Rashid (2010) determined that the size and

number of stomata were reduced in Z. mays along with decreased size of guard cells,

leading to a decrease in Z. mays growth (17).

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development. It is report that only young, newly grown wheat exemplify chlorosis

characteristic, while mature, developed wheat retain their dark green color during Ca

deficiency (5)

In addition, the stem height and fibrous root length were roughly similar to the

control treatment. This result is not consistent with other studies. Lascaris and Deacon

(1991) stated that calcium deficiency enhance the rate of root cortical death (RCD),

causing the root and shoot to become reduce (23).

Effect of Magnesium Deficiency

When wheat plantendured magnesium deficiency, there was a reduction in seed

germination and stem height. However, the fibrous root length and weight increased.

Also, the wheat plantexhibit chlorosis at the tip of the leaf.

Furthermore, chlorosis and reduced shoot system is consistent with other studies

(24,5). The cause of chlorosis is by the disruption of the photosynthetic process,

particular, by the decrement of the Hill reaction activity and RuBP carboxylase activity

(25)

Studies do not support the result of the experiment, in which the fibrous root

length and weight increased. It has been report that Mg-deficient wheat plant endure

restricted root growth (24,5).

Effect of Micronutrient

The micronutrient-deficient wheatdid not demonstrate any visible signs or

symptoms in the stem or root of the plant. In addition, the stem height was similar to the

control treatment. However, the length of the fibrous root and weight of the plant

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increased in comparison the control group. It is difficult to distinguish which

micronutrient (e.g. Fe, Cl, Cu, CO, Mg, Mn, B, Mo, and Zn) would have an adverse

effect on the growth and development of wheat plant. Many literature studies focus on

the effect one particular micronutrient deprivation. In addition, limit amount of studies

were performed on depriving plant of all micronutrients. Each nutrient deficiencies have

various effect on the germination of wheat. Some mineral deficiency have contradicting

effects. For example, low boron concentration has been show to increase weight of

shoot and root system of wheat plant (26). On the contrary, Kleli, Eker,and Cakmak

(2004) showed that zn deficiency decrease shoot weight in wheat (27). Therefore, it is

challenging to determine which minerals have a greater influence on the growth and

development of wheat plant.

Further improvement can be made for future experiment. First, the plants were

not given the same amount of nutrient-enhanced water. Giving a plant more or less

nutrient-filled water could restrict plant growth and development (3). Not to mention,

Lawson and Blatt (2014) stated that the stomata of well watered plants...reduce

photosynthetic rates, which further reduces the plant ability to grow (28). For these

reason, a discrete amount of water must be establish. Secondly, a larger sample size is

require to determine if the experiment is valid. In this experiment, only one sample pot

was used for each deficiencies (including the control). This does not give a excellent

representation of all wheat plant and, therefore, additional sample must be included.

Thirdly, the wheat plant were not fully developed due to time constraint. In order to

possess an accurate examination, the wheat plant should be allow to develop into a

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mature plant. Not to mention, some deficiencies, such as potassium, do not appear until

maturity (29). Therefore, the time span of the experiment should increase.

All and all, nutrient deficiency can induce unique physiological and morphological

changes. Such changes can be seen via leaf appearance along with morphological and

phenotypical changes of the root and shoot system. Future investigation should include

additional control, a larger sample size, and an extension on the duration to allow

maturity. In addition, further experiment should be conducted on the different

concentration for each macro- and micronutrient.

Lastly, study of nutrient deficient wheat plantprovide an opportunity to improve

agricultural methods and increase crop productivity. For instance, there is a challenge

for agriculture to meet the worlds increasing demand. To meet such challenge require

to uptake more land for further cultivation or to increase yield under restricted area.

Improper management of plant nutrient have further provoke the problem. Therefore,

understanding the consequence of nutrient deficiency can provoke people to make a

change.

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Nutrient deficiency cause morphological and phenotypic responses in Wheat