Why proline imino acid

Like in bacteria, proline transporters also act as glycinebetaine transporters in plants but with different affinities. Though intracellular localization, substrate selectivity, and affinity of the three AtProTs are similar, they exhibited differential expression patterns in various plant organs indicating differential transport of these molecules.

By fusing transporter genes with GUS, they demonstrated that AtProT1 , AtProT2 , and AtProT3 are localized in lignified tissues like phloem of all organs, epidermis, and cortex of roots and in epidermis of leaves respectively, Grallath et al. ProT1 isolated from tomato has shown to be expressed specifically in pollen grains Schwacke et al. Further, Lehmann et al. In spite of the fact, that single, double, and triple knockout mutants of the AtProT1 , AtProT2 , and AtProT3 genes responsible for proline transport in plants have been isolated and characterized, these mutants did not reveal any differences when compared to wild type plants Lehmann et al.

This underlays the complex situation and therefore needs further elucidation. Along with glutamate, amino acid permease AAP family mediates proton coupled uptake of neutral amino acids such as proline Frommer et al. Couturier et al. PtAAP11 was highly expressed in differentiating xylem cells in different organs. Further, functional characterization revealed that it is a high affinity amino ATF, more particularly for proline.

Therefore, the authors suggested that PtAAP11 may play an important role in xylogenesis by providing proline which is required for xylem cell wall proteins in poplar. Lysine-histidine transporter LHT family transports neutral and acidic amino acids including proline Lee and Tegeder, The fact that both low and high affinity-proline transporters exist in plants implicate that they play a role in general transfer of nitrogen and also proline for its specific functions in different cells and tissues.

In summary, proline transporters AAPs play an important role in plant development by providing proline as a source of nitrogen and energy which is required for lignifications, xylem differentiation and cell wall modification during plant development as a component of plant cell wall proteins. But the exact mechanisms how proline can mediate these functions are not known. TABLE 2. The amount of free proline and its metabolism modulates transition to flowering, pollen, and embryo development.

In support of it, concomitant expression of genes encoding enzymes of proline metabolism was observed in seeds Armengaud et al. It was noticed that P5CS2 is expressed mostly in actively dividing meristematic cells, developing tissues, callus, and cell suspension cultures.

Their experiments indicated exogenous proline can rescue p5cs2 mutants by ex vivo cultivation of developing seeds, but the mutant plants undergo aberrant development and become sterile.

It has also been reported that homozygous p5cs2 mutant plants died before the onset of flowering. Therefore, specific role of P5CS2 in reproductive development could not be analyzed Szekely et al. When Arabidopsis plants were simultaneously silenced or co-suppressed with P5CS1 and P5CS2 genes, they resulted in retarded growth, delayed flowering and reduced apical dominance Nanjo et al.

The above results indicate that Arabidopsis P5CS1 is insufficient for compensation of developmental defects caused by knockout of P5CS2. Taken together, the data demonstrate that these two genes have non-redundant functions in plants. Thus, these results emphasize the role s of P5CS in pollen fertility. It has been found that P5CS2 is not essential for sexual reproduction Funck et al.

They obtained homozygous p5cs2 mutants that are viable and could produce fertile seeds by in vitro culture of immature mutant seeds on MS medium supplemented with 60 mM sucrose and 2 mM proline. This allowed generating homozygous plants that are phenotypically normal, but showed reduced growth compared to the wild type plants.

Under short day and low-light conditions, these plants produced viable seeds. It has been found that p5cr mutations cause embryonic lethality, however. They reported arrest of the embryo development after the second division of the embryo proper in p5cr mutants. All attempts to rescue putative homozygous p5cr mutant embryos in vitro by proline feeding failed.

Their efforts to promote embryo development of homozygous seeds in siliques of heterozygous parents in situ by feeding the proline exogenously or induction of internal proline accumulation through salt stress were not fruitful.

Proline not only participates in protein synthesis, but regulates several important functions like osmotic adjustment and protection of proteins during stress conditions. Its multifarious functions are always enigmatic in plants. Deficiency in proline biosynthesis leads to abnormal plants and cell wall defects, thus implicating its role in structural proteins.

But, clear evidence is lacking for attributing several specific functions to this amino acid. Unless such maps are available along with their experimental validation, we cannot pinpoint the exact metabolic functions of proline other than its role in primary metabolism in protein biosynthesis.

All the authors of the manuscript meet the essential criteria of the publication. All authors have read and approved the manuscript.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Alm, J. Preference of cabbage white butterflies and honey bees for nectar that contains amino acids. Oecologia 84, 53— Armengaud, P.

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They, along with glycine and L -proline , are the chief amino acids that make up spider silk proteins. In the past month, chemists at San Diego State University and Northwestern University Evanston, IL discovered that before spiders spin their silk, they store the silk proteins in complex nanoparticles. Learn more about this molecule from CAS , the most authoritative and comprehensive source for chemical information.

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