Shoot growth in Ilex paraguariensis plants grown under varying photosynthetically active radiation is affected through gibberellin levels

Abstract

Ilex paraguariensis (yerba mate) is a speciesnative to South America of economic importance. Plants of yerba mate were grownfor 35 days in pots under photosynthetically active radiation (PAR) atintensities varying between 1, 4, 20, 50 and 100% of full sunlight in order tostudy growth in relation to gibberellins. Internode length of new shootsincreased under lower PAR. Uniconazole and Prohexadione-Ca (inhibitors ofgibberellin biosynthesis) inhibited shoot length under all light intensities,suggesting that increased levels of gibberellins active on shoot growth mayaccount for longer internodes in shaded plants. Gibberellin A1 andA3 were identified in shoots by capillary gas chromatography-massspectrometry. Increased levels of the GA1 + GA3 pool(measured by gas chromatography-selected ion monitoring with deuterogibberellins as internal standards) were found in shoots of plants grown underdecreasing PAR. However exogenous GA3 at 15, 150 and 1500mM was ineffective in reversing the stunting effect of 100% PAR.Inone experiment GA4 at 150 and 1500 mM lengthened theinternodes of plants grown under full sunlight comparable to those grown in theshade, suggesting a differential effect of “active” gibberellins ofdifferent molecular structure. These and previous results imply that thephotomorphogenetic control of shoot growth by light intensity in Ilexparaguariensis plants grown under different PAR is modulated throughthe levels of endogenous gibberellins.