Abstract
Phosphatases are widely found in plants having intracellular and extracellular activities. Phosphatases are believed to be important for phosphorous scavenging and remobilization in plants, but its role in adaptation to abiotic stresses and growth hormones at germination level has not been critically evaluated. To address this issue, the effect of ABA, GA3, NaCl and drought on germination, growth, acid and alkaline phosphatases in sorghum embryos and endosperm was investigated. Germination decreased markedly under ABA, NaCl and drought treatments. Subsequently, a remarkable decrease in fresh weight and dry weight was observed in embryos under ABA and NaCl treatments, whereas a significant decrease in endosperm fresh weight was observed only under drought stress. However, no significant change in endosperm dry weight was observed under other any treatment. Furthermore, a considerable increase in acid phosphatse activity was observed in embryos under GA3 and NaCl treatments, however, alkaline phosphatase activity was substantially higher under all treatments. In endosperm, a significant increase in acid phosphatase activity was observed under ABA and NaCl treatments. Alkaline phosphatse activity was apparently higher under GA3. However, no substantial changes in acid or alkaline phosphatase activities were observed after drought treatments. These findings suggest that changes in the phosphatase enzymes might play important roles in adaptation of germinating seeds, to changing environmental conditions. Based upon these results, a possible physiological role of phosphatases in germinating sorghum seeds is discussed. Keywords: Growth, sorghum, acid phosphatase, alkaline phosphatase.
Highlights
Water stress affects practically every aspect of plant growth and metabolism
The tissue water content (FW-dry weight (DW))/DW ratio, a measure of expansion growth of embryo in distilled water showed no substantial change with respect to ABA and GA3 treated embryos, a dramatic decrease was observed under NaCl treatment
A significant increase in acid phosphatase activity was observed after GA3 and NaCl treatment, a considerable decrease was observed in ABA-irrigated embryos (Table 4)
Summary
Plant responses to water deficit depend upon various factors such as duration and degree of stress, growth stage and time of stress exposure (Gupta and Sheoran, 1983) Due to their sedentary mode of life, plants resort to many adaptive strategies in response to different abiotic stresses such as high salt, dehydration, cold and heat, which affect the plant growth and productivity (Gill et al, 2003). Sorghum is a C4 grass that is well adapted to semiarid and arid tropics (Quinby, 1974) where salinity is the major problem due to limited water supply This grain crop is the fifth most important cereal grown worldwide, due in large parts to its unusual tolerance to adverse environmental conditions (Doggett, 1988). ABA and GA3 are well-documented regulators of germination, with GA generally having promotive effects and ABA having inhibitory effects on germination and related changes through multiple regulatory mechanisms, including transcriptional control and synthesis of specific enzymes (for review see Fincher, 1989)
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