Muhammad Mazhar Iqbal

Dynamic Proline Metabolism: Importance and Regulation in Water-Limited Environments

Abstract Proline is an important imino acid that accumulates in plants in response to different environmental constraints including water-limited conditions. The literature shows a positive association between proline accumulation and drought tolerance in plants. However, some recent findings highlighted that induction of drought tolerance in plants is not only due to proline accumulation and turnover, but also due to metabolism of proline that is responsible for maintaining plant growth during drought conditions. Plants mutant for enzymes involved in the biosynthesis Δ1-pyrroli [pyrroline-5-carboxylate synthetase 1 (P5CS1)] and catabolism [proline dehydrogenase 1 (ProDH1)] of proline exhibited significant growth reduction under drought conditions. Plants exposed to drought show accumulation of proline that in turn maintains the redox status. A variety of cellular processes mediate the biosynthesis and catabolism of proline. Presently, only a few mechanisms dealing with this imino acid are fully elucidated. For instance, highly abscisic acid (ABA)-induced protein phosphatase 2Cs differentially influenced the endogenous levels of PDH1 and P5CS1 proteins apart from the same increase in the cellular levels of proline. Proline biosynthetic (P5CS1) and catabolic (PDH1) genes are regulated via some posttranslational changes that are not fully known. In this chapter, we have discussed proline metabolism in plants under limited water regimes. We have also provided the details of proline association with other key physiochemical attributes under water deficit conditions.

Calcium Carbide-induced Changes in Germination, Morpho-phenological and Yield Traits in Cucumber (Cucumis sativus)

Calcium carbide (CaC2) is a well-known source of acetylene and ethylene gases. Its use as a plant growth regulator could be an innovative approach for vegetable production if applied in suitable formulation. Different rates of CaC2 (10, 20, 30 and 40 mg plate) were evaluated regarding seed germination and morphological characteristics under controlled conditions. The results showed that germination rate was significantly improved by using low rates of CaC2 (10 to 30 mg CaC2 plate) while the highest rate of CaC2 (40 mg plate) suppressed germination rate of cucumber seeds. Likewise, lower rates of CaC2 were also found effective in enhancing the root and hypocotyl lengths, number of lateral roots and fresh weight of seedling while the highest rate of CaC2 was proved inhibitory. It was recorded that the CaC2 induced improvement in seed germination was significantly correlated (r = 0.75) with magnitude of ethylene production during imbibition. Moreover, a pot experiment was conducted under natural conditions to select optimum rate and coating material of CaC2 regarding growth and yield parameters of cucumber. It was found that all rates of CaC2, irrespective of coating materials, exhibited new primary branches, early female flowering and fruit maturity. Maximum response regarding female flower count, fruit yield and ethylene emission was obtained by the application of paint coated CaC2 at 300 mg pot, which resulted in 34% more fruit yield compared to control plants.