Proline has long been known to accumulate in plants experiencing water limitation and this has driven studies of proline as a beneficial solute allowing plants to increase cellular osmolarity during water limitation. Proline metabolism also has roles in redox buffering and energy transfer and is involved in plant pathogen interaction and programmed cell death. Some of these unique roles of proline depend on the properties of proline itself, whereas others depend on the “proline cycle” of coordinated proline synthesis in the chloroplast and cytoplasm with proline catabolism in the mitochondria. The regulatory mechanisms controlling proline metabolism, intercellular and intracellular transport and connections of proline to other metabolic pathways are all important to the in vivo functions of proline metabolism. Connections of proline metabolism to the oxidative pentose phosphate pathway and glutamate-glutamine metabolism are of particular interest. The N-acetyl glutamate pathway can also produce ornithine ...

https://bioone.org/journals/the-arabidopsis-book/volume-2010/issue-8/tab.0140/Proline-Metabolism-and-Its-Implications-for-Plant-Environment-Interaction/10.1199/tab.0140.pdf

Proline Metabolism and Its Implications for Plant-Environment Interaction

Electrolyte leakage and lipid degradation account for cold sensitivity in leaves of Coffea sp. plants.

Effect of Drought Stress on Lipid Metabolism in the Leaves of Arabidopsis thaliana (Ecotype Columbia)

Nitrogen is a limiting resource for plant growth in most terrestrial habitats since large amounts of nitrogen are needed to synthesize nucleic acids and proteins. Among the 21 proteinogenic amino acids, arginine has the highest nitrogen to carbon ratio, which makes it especially suitable as a storage form of organic nitrogen. Synthesis in chloroplasts via ornithine is apparently the only operational pathway to provide arginine in plants, and the rate of arginine synthesis is tightly regulated by various feedback mechanisms in accordance with the overall nutritional status. While several steps of arginine biosynthesis still remain poorly characterized in plants, much wider attention has been paid to inter- and intracellular arginine transport as well as arginine-derived metabolites. A role of arginine as alternative source besides glutamate for proline biosynthesis is still discussed controversially and may be prevented by differential subcellular localization of enzymes. Apparently, arginine is a precursor for nitric oxide (NO), although the molecular mechanism of NO production from arginine remains unclear in higher plants. In contrast, conversion of arginine to polyamines is well documented, and in several plant species also ornithine can serve as a precursor for polyamines. Both NO and polyamines play crucial roles in regulating developmental processes as well as responses to biotic and abiotic stress. It is thus conceivable that arginine catabolism serves on the one hand to mobilize nitrogen storages, while on the other hand it may be used to fine-tune development and defense mechanisms against stress. This review summarizes the recent advances in our knowledge about arginine metabolism, with a special focus on the model plant Arabidopsis thaliana, and pinpoints still unresolved critical questions.

https://kops.uni-konstanz.de/bitstream/handle/123456789/31996/Winter_0-302191.pdf;sequence=3

Physiological implications of arginine metabolism in plants.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/j.febslet.2011.05.018

A chloroplast pathway for the de novo biosynthesis of triacylglycerol in Chlamydomonas reinhardtii

Effects of water stress on lipid metabolism in cotton leaves

Mitochondrial carrier family proteins are diverse in their substrate specificity, organellar location, and gene expression. In Arabidopsis (Arabidopsis thaliana), 58 genes encode these six-transmembrane-domain proteins. We investigated the biological role of the basic amino acid carrier Basic Amino Acid Carrier2 (BAC2) from Arabidopsis that is structurally and functionally similar to ARG11, a yeast ornithine and arginine carrier, and to Arabidopsis BAC1. By studying the expression of BAC2 and the consequences of its mutation in Arabidopsis, we showed that BAC2 is a genuine mitochondrial protein and that Arabidopsis requires expression of the BAC2 gene in order to use arginine. The BAC2 gene is induced by hyperosmotic stress (with either 0.2 m NaCl or 0.4 m mannitol) and dark-induced senescence. The BAC2 promoter contains numerous stress-related cis-regulatory elements, and the transcriptional activity of BAC2:β-glucuronidase is up-regulated by stress and senescence. Under hyperosmotic stress, bac2 mutants express the P5CS1 proline biosynthetic gene more strongly than the wild type, and this correlates with a greater accumulation of Pro. Our data suggest that BAC2 is a hyperosmotic stress-inducible transporter of basic amino acids that contributes to proline accumulation in response to hyperosmotic stress in Arabidopsis.

Mutations in the Hyperosmotic Stress-Responsive Mitochondrial BASIC AMINO ACID CARRIER2 Enhance Proline Accumulation in Arabidopsis

The effects of water stress on [1-14C]-oleic and [1-14C]-linoleic acid desaturations were studied in leaves of two varieties of cotton (Gossypium hirsutum L.), one drought-sensitive (Reba) and the other more resistant (Mocosinho). After 24 h incorporation, [1-14C]-oleate led to the appearance of linoleate in phospholipids and, additionally, of linolenate in galactolipids. [1-14C]-Linoleate was desaturated to linolenate only in galactolipid fractions. Water stress markedly inhibited the incorporation of the precursors into the leaf lipids. The two desaturation steps were affected, particularly the transformation of linoleate to linolenate in monogalactosyldiacylglycerol in the drought-sensitive variety of cotton. The metabolic implications of the inhibition of the biosynthesis of C18-polyunsaturated fatty acids are discussed.

Anne Marie Justin

Papers

Effects of water stress on lipid metabolism in cotton leaves

Mutations in the Hyperosmotic Stress-Responsive Mitochondrial BASIC AMINO ACID CARRIER2 Enhance Proline Accumulation in Arabidopsis

Effects of drought on [1-14C]-oleic and [1-14C]-linoleic acid desaturation in cotton leaves

Biosynthesis of eukaryotic lipid molecular species by the cyanobacterium Spirulina platensis.