Evaluation of foliar application of Methanol effects on some morphological, physiological and biochemical indices of Lentil (Lens culinaris Medik.) under water deficit stress

IntroductionLentil (Lens culinaris Medik.) is a good source of protein, carbohydrates as well as minerals, vitamins and unsaturated fatty acids as such it plays an important role in the human diet and cultivated worldwide. Water shortage is one of the most important abiotic factors that can limit morphological, physiological, yield, and plant distribution. Legumes such as lentil are highly sensitive to water stress. According to references, increasing the concentration of CO2 can neutralize the effects of water stress on plants. One of the ways for increasing the concentration of CO2 in plants is using compounds such as methanol, ethanol, propanol, butanol, and the glycine amino acids, glutamate and aspartate. Methanol is oxidized to formaldehyde and CO2, and further synthesized into sugars and amino acids, including serine and methionine, in tissues of various C3 plants. In plants, methanol can arise from a number of sources; for example, from pectin de-methylation in cell walls, protein repair pathways and lignin degradation. Metabolism of methanol is less understood in plants. The identity of enzymes that oxidize methanol to formate in plants is unclear yet. However, positive growth effects of methanol have been reported earlier in a variety of C3 plants like wheat, barley, mung bean, chickpea, bean, tomato and cotton. Research has shown that plants respond to water deficit stress by accumulations of soluble materials in cells. Most compatible compounds contain soluble proteins, sorbitol, organic acids, proline content and ions such as K and Ca. K deficiency in plants leads to reduced Rubisco activity, stomatal conductance and an increase of reactive oxygen species (ROS), which ultimately reduces photosynthesis. As water stress is one of the major problems for production in the agricultural in Iran. The aims of this study were to determine: (1) whether foliar application of methanol can be improve the negative effects of water deficit stress in lentil and (2) determine the most effective methanol concentration for foliar application.
Materials and MethodsTo evaluate the effects of foliar application of methanol and water deficit stress on morpho-physiological and biochemical characteristics of lentil, a factorial experiment based on completely randomized design with three replications was performed. The treatments included methanol solution at four levels (0, 10, 20 and 30% v/v) and water stress included severe water stress (25% of field capacity), moderate water stress (75% of field capacity) and non-stress (100% of field capacity). Lentil seeds (Ghachsaran cultivar) were sown in a standard petri dish in a germinator chamber. When the seedlings reached a height of 5 cm, they were transplanted at a rate of three seedlings per pot and the pots were placed in a growth chamber. The foliar application of methanol was applied at three times during growth season of lentil, with 10 days intervals. The first foliar application of methanol was performed in early seedling stage (4 weeks after planting). Second and third methanol applications were given ten days after first application in flowering and podding stages, respectively. Measurements were taken for the morpho-physiological traits were: plant height, number of leaves, number of pods, leaf area, shoot and leaf dry weights, relative water content (RWC), membrane stability index (MSI) and nutrient concentration of leave (Na,K and Ca). Biochemical traits such as proline content, soluble proteins and antioxidant enzyme activity were measured.
Results and DiscussionAll of the morphological traits were mainly affected by severe water stress. Under non-stress and moderate water stress, methanol treatments had significantly increasing of the morphological traits. Methanol treatments induced a significant increase in MSI and RWC comparing with control under all of water stress treatments. Methanol treatments increased proline content and total soluble protein under severe and moderate water stress comparing with control treatments. Foliar application of methanol had no significant effects on concentration of elements (Na, K and Ca) in leaf and also in antioxidant enzyme activity. Plants are easily able to absorb methanol sprayed on leaves then used by the plant as a source of carbon. In comparison with CO2, methanol is formed of relatively smaller molecules and it is more easily absorbed and used by plants. Therefore, as a carbon source, methanol can play a role in developing CO2 assimilation and net-photosynthesis. An investigation on flax, reported that spraying a solution of methanol might have stimulated growth and increased height in the treated plants by increasing cytokinin levels and cell division. Coexisting bacteria like methylotrophic live on the leaves of most crops; these bacteria, for receiving methanol that gets out of the plant's leaf, give the construction precursor of some hormones like auxin, cytokinin to the plant in order to accelerate the growth and physiological process. Reports have mentioned that application of methanol on aerial parts of cultivated plants led to a significant increase in the morpho-physiological traits, acceleration of ripeness, reduced effect of water deficit stress and reduced water requirement.
Conclusion Results of this research indicated that application of methanol has significantly increasing in the lentil morpho-physiological traits, proline content and leaf soluble protein under moderate and severe stress. Concentrations of leaf elements such as K, Ca and Na and antioxidant enzymes activity were not affected by methanol foliar application. Methanol application at 25% (volumetric percentage) were effective than the other treatments. According to the results, using of methanol is recomended to reduce the negative effects of water deficit stress in lentil plant.