A Novel Effect for Glycine on Root System Growth of Habanero Pepper

Abstract

<jats:p>Amino acids, a major fraction of the low-molecular-weight organic nitrogen in soil, act as signaling molecules that indicate the presence of nutrient-rich patches to the roots. To characterize the effects of amino acids on root growth, we used seedlings of habanero pepper (<jats:italic>Capsicum chinense</jats:italic>), one of the most widely cultivated annual spice crops in the world. We tested the effect of L-glutamate, L-aspartate, and glycine on the primary root of seedlings grown aseptically under different conditions of pH and light. L-glutamate and L-aspartate did not inhibit the root growth of habanero pepper. In contrast, glycine inhibited the growth of roots, stimulated root hair growth, and induced a significant accumulation of starch grains in the root apex. The use of aminoethoxyvinylglycine, an inhibitor of ethylene biosynthesis, and the evaluation of <jats:italic>1-aminocyclopropane-1-carboxylic acid oxidase</jats:italic> expression provided evidence of a role for ethylene in the root responses to glycine. We suggest that these changes in the root apex in response to exogenous glycine could be an important adaptive response that allows plants to efficiently access the fluctuating availability of nutrients in the soil.</jats:p>

Exogenous glycine inhibits root elongation and reduces nitrate-N uptake in pak choi (Brassica campestris ssp. Chinensis L.)

“…One important finding of this study is that application of an ethylene biosynthesis inhibitor (0.5 or 1 μM AVG) or perception blocker (10 μM AgNO 3 ) to NaNO 3 + Gly-treated pak choi markedly alleviated the inhibition of primary root length under agar plate conditions ( Fig 5 and S5 Fig ). These findings are in agreement with Domínguez-May et al (2013), who suggested that ethylene played a regulatory role in the inhibitory effects of Gly in habanero pepper [ 24 ]. Moreover, we also showed that exogenous application of 0.5 μM AVG and 10 μM AgNO 3 could markedly increase the 15 NO 3 - -N uptake rate in hydroponically grown pak choi seedlings in response to NaNO 3 + Gly (Figs 6 and 7 ).…”

“…In both the agar plate and hydroponic systems, exogenous Gly significantly reduced primary root length ( Fig 1A, 1C and 1D , Fig 2A and S1 Fig ). This is similar to the effects of single amino acids, such as L -Glu and Gly [ 21 , 24 , 45 ] and mixtures of N sources supplied with NO 3 - -N and L -Glu [ 19 , 20 ] on plants grown on agar plates. Only Walch-Liu, Forde (2008) and Leblanc et al (2013) have investigated the effect of Glu on root development in the presence of both NO 3 - -N and Glu; the mixtures used in those studies more closely resemble soil conditions.…”

“…However, despite N being taken up at a similar rate, the root length and shoot growth of exogenous Gly-treated seedlings were significantly impaired by Gly ( Fig 2 and S3 Fig ). Phytohormones have been demonstrated to be involved in growth inhibition [ 24 , 54 ]. In this study, the growth retardation induced by Gly may be related to altered phytohormone levels.…”

“…For instance, L -glutamate (Glu) suppresses primary root length [ 21 – 23 ]. Moreover, while the effects of L -Glu on root morphology are relatively well understood; few studies have investigated the response of roots to Gly, a model amino acid in organic N studies [ 24 , 25 ], and the regulatory interactions between Gly and inorganic N on root growth. Therefore, additional studies on the effects of amino acid N sources on the root morphology of leafy vegetables are necessary.…”

“…Similarly, Li et al (2013) reported that NH 4 + -N inhibited Arabidopsis thaliana lateral root formation by inducing production of ethylene [ 34 ]. Domínguez-May et al (2013) suggested that ethylene also plays a role in the reduced root length induced by Gly in habanero pepper [ 24 ]. In addition, NO 3 - -N uptake is also regulated by ethylene in the presence of N sources.…”