Induction of xylem sap methylglycine by a drought and rewatering treatment and its inhibitory effects on the growth and development of plant organs

Abstract

In higher plants, the xylem vessels functionally connect the roots with the above‐ground organs. The xylem sap transports various organic compounds, such as proteins and amino acids. We examined drought and rewatering‐inducible changes in the amino acid composition of root xylem sap collected from Cucurbita maxima roots. The major free amino acids in C. maxima root xylem sap were methylglycine (MeGly; sarcosine) and glutamine (Gln), but MeGly was not detected in the xylem sap of cucumber. MeGly is an intermediate compound in the metabolism of trimethylglycine (TMG; betaine), but its physiological effects in plants are unknown. Drought and rewatering treatment resulted in an increase in the concentration of MeGly in root xylem sap to 2.5 mM. After flowering, the MeGly concentration in the xylem sap dropped significantly, whereas the concentration of Gln decreased only after fruit ripening. One milli molar MeGly inhibited the formation of adventitious roots and their elongation in C. maxima, but glycine, dimethylglycine, or TMG had no effect. Similar effects and the inhibition of stem elongation were observed in shoot cuttings of cucumber and Phaseolus angularis. These observations seem to imply a possible involvement of xylem sap MeGly in the physiological responses of C. maxima plants to drought stress.

Metabolomic Study of Chardonnay Grapevines Double Stressed with Esca-Associated Fungi and Drought

“…Trigonelline has been shown to increase in response to oxidative, UV, and salt stresses, and has been proposed to act as an osmoregulator and to be an inducer of defense metabolism (Ashihara et al 2015;Berglund 1994;Minorsky 2002;Tramontano and Jouve 1997). Sarcosine (also known as methylglycine, being a derivative of the amino acid glycine) has been found in root xylem sap and implicated in the physiological response of Cucurbita maxima to drought (Oda et al 2005). Branched-chain amino acids (isoleucine, leucine, and valine), proline, and phenylalanine have been described to increase in response to water stress in several plants, including grapevine, and are considered to be associated with drought tolerance (Bowne et al 2012;Hochberg et al 2013;Semel et al 2007;Witt et al 2012).…”

Organic substances in xylem sap delivered to above-ground organs by the roots

“…One reason for this may be that abscisic acid synthesized in shoot vascular tissues is transported via phloem to the roots and is transferred to xylem in the root central cylinder by an unknown mechanism. Other organic substances in xylem sap have been identified as lower molecular weight substances, including amino acids (Oda et al 2005), sugars (Iwai et al 2003;Satoh et al 1992), and organic acids (Hibberd and Quick 2002;Ma and Hiradate 2000), and as macromolecules, including oligo-and polysaccharides (Iwai et al 2003) and proteins (Buhtz et al 2004;Kehr et al 2005;Rep et al 2002Rep et al , 2003Satoh et al 1992). Recent results are summarized in Tables 1, 2, and 3.…”

Cadmium toxicity induced contrasting patterns of concentrations of free sarcosine, specific amino acids and selected microelements in two Noccaea species

“…The AA sarcosine (Sar, N-methylglycine) is an intermediate of trimethylglycine (glycine betaine). Glycine betaine is known to be a metabolite that accumulates during oxidative stress [ 29 ]; therefore, Sar declines as a result of the methylation of Sar [ 30 ] or due to the lack of Gly caused by the reaction of Gly and choline [ 31 ]. Thus, a decline in Sar is related to the biosynthesis of glycine betaine and plant defence against oxidative stress.…”