Potato (Solanum tuberosum L.) is a good source of dietary antioxidants. Chlorogenic acid (CGA) and caffeic acid (CA) are the most abundant phenolic acid antioxidants in potato and are formed by the phenylpropanoid pathway. A number of CGA biosynthetic routes that involve hydroxycinnamoyl-CoA quinate hydroxycinnamoyl transferase (HQT) and/or hydroxycinnamoyl-CoA shikimate/quinate hydroxycinnamoyl transferase (HCT) have been proposed, but little is known about their path in potato. CA production requires a caffeoyl shikimate esterase (CSE), and CA serves as a substrate of lignin precursor ferulic acid via the action of caffeic/5-hydroxyferulic acid O-methyltransferase (COMT I). CGA is precursor of caffeoyl-CoA and, via caffeoyl-CoA O-methyltransferase (CCoAOMT), of feruloyl-CoA. Feruloyl-CoA is required for lignin and suberin biosynthesis, crucial for tuber development. Here, metabolite and transcript levels of the mentioned and related enzymes, such as cinnamate 4-hydroxylase (C4H), were determined in the flesh and skin of fresh and stored tubers. Metabolite and transcript levels were higher in skin than in flesh, irrespective of storage. CGA and CA production appear to occur via p-coumaroyl-CoA, using HQT and CSE, respectively. HCT is likely involved in CGA remobilization toward suberin. The strong correlation between CGA and CA, the correspondence with C4H, HQT, CCoAOMT2, and CSE, and the negative correlation of HCT and COMT I in potato tubers suggest a major flux toward suberin.
Abbreviations: PA, phosphatidic acid; PLD, phospholipase D; ROS, reactive oxygen species.Phospholipase D (PLD) is involved in different plant processes, ranging from responses to abiotic and biotic stress to plant development. Phospholipase Dd (PLDd) is activated in dehydration and salt stress, producing the lipid second messenger phosphatidic acid. In this work we show that pldd Arabidopsis mutants were more tolerant to severe drought than wild-type plants. PLDd has been shown to be required for ABA regulation of stomatal closure of isolated epidermal peels. However, there was no significant difference in stomatal conductance at the whole plant level between wild-type and pldd mutants. Since PLD hydrolyses structural phospholipids, then we looked at membrane integrity. Ion leakage measurements showed that during dehydration of leaf discs pldd mutant has less membrane degradation compared to the wild-type. We further analyzed the mutants and showed that pldd have higher mRNA levels of RAB18 and RD29A compared to wild-type plants under normal growth conditions. Transient expression of AtPLDd in Nicotiana benthamiana plants induced a wilting phenotype. These findings suggest that, in wt plants PLDd disrupt membranes in severe drought stress and, in the absence of the protein (PLDd knock-out) might drought-prime the plants, making them more tolerant to severe drought stress. The results are discussed in relation to PLDd role in guard cell signaling and drought tolerance.
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