Physiology of the Yellow-Green 6 Gene in Tomato: A Possible Interrelationship between the Phenotypic Expressions of the Yellow-Green 6 Gene Mutation and the Gibberellins

Effects of gibberellic acid on primary terpenoids and delta-tetrahydrocannabinol in Cannabis sativa at flowering stage

Plants synthesize an astonishing diversity of isoprenoids, some of which play essential roles in photosynthesis, respiration, and the regulation of growth and development. Two independent pathways for the biosynthesis of isoprenoid precursors coexist within the plant cell: the cytosolic mevalonic acid (MVA) pathway and the plastidial methylerythritol phosphate (MEP) pathway. However, little is known about the effects of plant hormones on the regulation of these pathways. In the present study we investigated the effect of gibberellic acid (GA(3)) on changes in the amounts of many produced terpenoids and the activity of the key enzymes, 1-deoxy-D-xylulose 5-phosphate synthase (DXS) and 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), in these pathways. Our results showed GA(3) caused a decrease in DXS activity in both sexes that it was accompanied by a decrease in chlorophylls, carotenoids and Delta(9)-tetrahydrocannabinol (THC) contents and an increase in alpha-tocopherol content. The treated plants with GA(3) showed an increase in HMGR activity. This increase in HMGR activity was followed by accumulation of stigmasterol and beta-sitosterol in male and female plants and campestrol in male plants. The pattern of the changes in the amounts of sterols was exactly similar to the changes in the HMGR activity. These data suggest that GA(3) can probably influence the MEP and MVA pathways oppositely, with stimulatory and inhibitory effects on the produced primary terpenoids in MVA and DXS pathways, respectively.

The isolation and characterization of gibberellin-deficient mutants in tomato

In tomato, nine independent EMS-induced mutants representing recessive mutations at three different loci (gib-1, gib-2, and gib-3) were isolated. Six of these have an almost absolute gibberellin requirement for seed germination and elongation growth. In addition, the leaves are darker green, smaller, and changed in structure as compared to wild type. The three other mutants, which germinate without GA, are allelic to specific, nongerminating mutants and have less severe mutant characteristics. The respective loci are situated on three different chromosomes. The genes identified by these mutants control steps in gibberellin biosynthesis, as endogenous gibberellins are strongly reduced.

Gibberellic Acid effects on greening in pea seedlings

The effect of gibberellic acid (GA) on light-induced greening of etiolated pea plants (Pisum sativum [L.] cultivars Alaska and Progress) was characterized. Progress, a GA-deficient dwarf of Alaska, was found to accumulate chlorophyll and light harvesting chlorophyll protein associated with photosystem II (LHC-II) more rapidly than Alaska, Alaska treated with GA, or Progress treated with GA. A slightly lower chlorophyll content was noted after 24 hours of light induced greening for Alaska treated with GA relative to untreated Alaska. GA-treated Progress, Alaska, and GA-treated Alaska all gave essentially identical patterns for LHC-II accumulation. Similar patterns of LHC-II mRNA induction were found in all four treatments indicating that differences in mRNA induction did not cause differences in LHC-II accumulation. Chlorophyll and LHC-II accumulation in each treatment followed the same patterns of accumulation and a significant correlation (at the 0.01 level of significance) was found between chlorophyll and LHC-II content. Since Progress treated with GA accumulated LHC-II and chlorophyll in a manner similar to that of Alaska, it is clear that GA alters the process of greening either directly or indirectly.