Changes in seed water status as characterized by NMR in developing soybean seed grown under moisture stress conditions.

Changes in water status of developing seeds of Soybean (Glycine max L. Merrill.) grown under different moisture stress conditions were characterized by proton nuclear magnetic resonance (NMR)- spin-spin relaxation time (T2). A comparison of the seed development characteristics, composition and physical properties indicated that, characteristics like seed weight, seed number/ear, rate of seed filling increased with development stages but decreased with moisture stress conditions. The NMR- spin-spin relaxation (T2) component like bound water increased with seed maturation (40-50%) but decreased with moisture stress conditions (30-40%). The changes in seed water status to increasing levels of moisture stress and seed maturity indicates that moisture stress resulted in more proportion of water to bound state and intermediate state and less proportion of water in free-state. These changes are further corroborated by significant changes in protein and starch contents in seeds under high moisture stress treatments. Thus seed water status during its development is not only affected by development processes but also by moisture stress conditions. This study strongly indicated a clear moisture stress and development stage dependence of seed tissue water status in developing soybean seeds.

Pre-treatment of seeds with static magnetic field ameliorates soil water stress in seedlings of maize (Zea mays L.).

The effect of magnetic field (MF) treatments of maize (Zea mays L.) var. Ganga Safed 2 seeds on the growth, leaf water status, photosynthesis and antioxidant enzyme system under soil water stress was investigated under greenhouse conditions. The seeds were exposed to static MFs of 100 and 200 mT for 2 and 1 h, respectively. The treated seeds were sown in sand beds for seven days and transplanted in pots that were maintained at -0.03, -0.2 and -0.4 MPa soil water potentials under greenhouse conditions. MF exposure of seeds significantly enhanced all growth parameters, compared to the control seedlings. The significant increase in root parameters in seedlings from magnetically-exposed seeds resulted in maintenance of better leaf water status in terms of increase in leaf water potential, turgor potential and relative water content. Photosynthesis, stomatal conductance and chlorophyll content increased in plants from treated seeds, compared to control under irrigated and mild stress condition. Leaves from plants of magnetically-treated seeds showed decreased levels of hydrogen peroxide and antioxidant defense system enzymes (peroxidases, catalase and superoxide dismutase) under moisture stress conditions, when compared with untreated controls. Mild stress of -0.2 MPa induced a stimulating effect on functional root parameters, especially in 200 mT treated seedlings which can be exploited profitably for rain fed conditions. Our results suggested that MF treatment (100 mT for 2 h and 200 for 1 h) of maize seeds enhanced the seedling growth, leaf water status, photosynthesis rate and lowered the antioxidant defense system of seedlings under soil water stress. Thus, pre sowing static magnetic field treatment of seeds can be effectively used for improving growth under water stress.

Proton NMR transverse relaxation time and membrane stability in wheat leaves exposed to high temperature shock.

Electrolyte leakage from leaves and NMR transverse relaxation time (T2) of leaf water were used to differentiate between heat-tolerant (NIAW 845) and susceptible (HD 2428) wheat (Triticum aestivum L.) cultivars. The leaves were exposed to high temperature shock in the range 30 to 55 degrees C and the damage caused, when evaluated by the two approaches was in close agreement. The critical temperature of injury leading to loss of membrane integrity was lower (39.1 degrees C) for susceptible cultivar, compared to tolerant cultivar (44.2 degrees C). Component analyses of NMR data revealed the existence of two fractions of cellular water in leaf tissues, namely, bound and free bulk water with distinct relaxation times. A dramatic reduction in the proportion of free water and a corresponding increase in bound water was observed in response to increase in temperature. This change in proportion occurred around 38 degrees C and 43 degrees C in HD 2428 and NIAW 845 respectively. The high temperature induced irreversible damage to cellular membrane integrity led to loss of compartmentation of cellular water fractions. The tolerant cultivar maintained its membrane integrity and cell water compartmentation until a temperature of 43 degrees C and susceptible could maintain it only until 38 degrees C.