Peroxisomes play diverse and important roles in plants. The functions of peroxisomes are dependent upon their steady state protein composition which in turn reflects the balance of formation and turnover of the organelle. Protein import and turnover of constituent peroxisomal proteins are controlled by the state of cell growth and environment. The evolutionary origin of the peroxisome and the role of the endoplasmic reticulum in peroxisome biogenesis are discussed, as informed by studies of the trafficking of peroxisome membrane proteins. The process of matrix protein import in plants and its similarities and differences with peroxisomes in other organisms is presented and discussed in the context of peroxin distribution across the green plants.
Polyamines (PAs) are positively charged molecules known to mitigate drought stress; however, little is known about their mechanism of alleviating drought stress. We investigated the effects of PAs exogenously applied as a seed primer and as a foliar spray on the growth, membrane stability (MS), electrolyte leakage (EL), Na ? and K ? cations, reactive oxygen species (ROS), catalase (CAT; EC 1.11.1.6) and guaiacol peroxidase (GPX; EC 1.11.1.7) activity and chloroplast ultra-structure in wheat (Triticum aestivum L.; cv. Sakha-94) under drought stress. Three PA solutions, namely, putrescine, spermine and a mixture of the two (Mix), were each applied at a concentration of 100 lM. Our study demonstrated that the retardation of chlorophyll loss and elevation of Rubisco levels were involved in PA-enhanced growth under drought stress. These relationships were mainly reflected in elevated fresh weight and dry weight in response to foliar spraying with all PA solutions and seed priming with the Mix solution. The elevated growth seemed to be due to increased photosynthetic pigments, protein and Rubisco. In contrast, drought decreased growth, photosynthetic pigments, protein and Rubisco. MS was enhanced by PAs applied as a seed primer or foliar spray, as shown by clear reductions in EL %, malondialdehyde (MDA) content and the Na ? /K ? ratio as well as reduced ROS markers and elevated CAT (but not GPX) activity. Further study showed that the Mix solution of PAs, applied either during seed priming or as a foliar spray, improved chloroplast ultra-structure, suggesting that improvements in Rubisco and photosynthetic pigments were involved in PA maintenance of chloroplast stability. Therefore, the present study showed that elevated CAT activity is the main mechanism through which PAs reduce ROS and MDA, thereby improving MS and protecting mesophyll cells structurally and functionally under drought stress in wheat.
Physiological parameters and expression levels of drought related genes were analyzed in early vegetative stage of two bread wheat cultivars (Sids and Gmiza) differ in drought tolerance capacity. Both cultivars were imposed to gradual water depletion started on day 17 till day 32 after sowing. Sids, the more tolerant cultivar to drought showed higher fresh and dry weights than the drought sensitive genotype, Gmiza. Under water stress, Sids had higher membrane stability index (MSI), lower accumulated H2O2 and higher activity of the antioxidant enzymes; catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX) and superoxide dismutase (SOD) than Gmiza. On the other hand, the differential expression patterns of the genes dhn, wcor and dreb were observed due to water deficit intensity according to cultivar’s tolerance to drought. The DNA sequence alignment of dun showed high similarity of about 80–92% identities with other related plants. The most striking overall observed trend was the highly induction in the expression of dun, wcor and dreb in leaves of the tolerant genotype, Sids under severe water stress.
Peroxisome biogenesis, peroxisome β-oxidation and antioxidant enzymes show conserved upregulation in response to ABA and water deficit-inducing treatments, highlighting an overlooked role for peroxisomes in response to drought.
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