PLASTID DEVELOPMENT IN GERMINATING WHEAT (TRITICUM-AESTIVUM) IS ENHANCED BY GIBBERELLIC-ACID AND DELAYED BY GABACULINE

Etioplast development and protochlorophyllide (Pchlide) accumulation w as studied in wheat seedlings (Triticum aestivum L. cv. Walde, Weibull ) grown in darkness on gibberellic acid (GA(3)), gabaculine (3-amino-2 ,3-dihydrobenzoic acid), or on a combination of the two. The results w ere compared with the features of seedlings grown on water only. GA(3) enhanced shoot growth and promoted etioplast development. A correlati on was observed between the appearance of prolamellar bodies (PLBs) an d of phototransformable Pchlide. Gabaculine, a known tetrapyrrole bios ynthesis inhibitor, delayed growth, slowed down the rate of PLB format ion and caused structural alterations of the etioplasts up to 48 h of germination. Gabaculine also delayed the formation of phototransformab le Pchlide as well as overall Pchlide biosynthesis, as deter mined by low-temperature fluorescence emission in vivo. The spectral blue-shift of newly formed chlorophyllide (Chlide) was delayed in irradiated dar k-grown gabaculine-grown seedlings, indicating an inhibited dissociati on of Chlide and NADPH-Pchlide oxidoreductase (Pchlide reductase; EC 1 .3.1.33). Thus there is a close correlation between accumulation of Pc hlide and etioplast development, also under conditions when developmen t is enhanced or delayed.