Expression of the le Mutation in Young Ovaries of Pisum sativum and Its Effect on Fruit Development

Abstract

l h e effect of the /e mutation on the growth and gibberellin (CA) content of developing fruits was investigated using the near-isogenic lines of fisum sativum L. 205+ (LeLe) and 205-(/ele). Although stem elongation is known to be reduced in 205-plants by approximately 65%, the growth of pods and seeds was unaffected by the /e mutation. CAI, CA,, and CAZo stimulated parthenocarpic development of unpollinated ovaries on both 205+ and 205-plants. GA2, was less active on 205-ovaries than on 205+, whereas CAI had similar, high activity i n both lines. The activity of CA, was even higher than that of CAI in both lines. Decapitation of 205+ plants induced parthenocarpic development of unpollinated ovaries, but this treatment was much less effective on 205-plants. l h e contents of CAI and GA, in entire ovaries 6 d after anthesis, as well as in the pod and fertilized ovules, were substantially lower in 205-than in 205' plants, whereas the reverse was true for the levels of CAzO and CAz9. lhese results suggest that 30-hydroxylation of CAzo to CAI is reduced i n ovaries as well as in vegetative tissues. Thus, the /e mutation appears to be expressed in young reproductive organs of the 205-line, even though it does not affect the fruit phenotype. Because the content of CAI i n the ovary was similar in the two lines, one explanation for the normal fruit size i n the 205-line is that CA, is the native regulator of pod growth. Alternatively, sufficient CAI may still be produced in 205-fruits to maintain normal pod growth.There is considerable evidence that fruit-set and pod development in Pisum sativum L. (garden pea) are regulated by GAs, which are probably supplied by the fertilized ovules (Eeuwens and Schwabe, 1975; Garcia-Martinez and Carbonell, 1980; Sponsel, 1982; Garcia-Martinez et al., 1987, 1991a. GAI, GA3, GAs, GA19, GAzo, and GAZ9 have been identified in ovules and pods of 4-d-old pollinated ovaries of pea cv Alaska, and GAI7, GAsl, and GA29 catabolite were identified additionally in the pods (Garcia-Marthez et al., 1987, 1991b). GAl, GA3, and GA20 induced parthenocarpic ovary growth in cv Alaska, with the order of activity GA3 > GA1 > GAZo (Sponsel, 1982; Garcia-Martínez et al., 1987).The contents of GAl and GA3 in pea ovaries are maximal during the time of rapid pod elongation (Garcia-Marthez et al., 1991b), suggesting that these GAs are involved in the regulation of fruit-set and development.Work with GA biosynthesis mutants indicates that GAI controls shoot elongation in maize, pea, and rice (Phinney, 1984), and a linear relationship was found between intemode length in pea and the logarithm of GA1 concentration in the shoot (Ross et al., 1989). The Le gene was shown to control the 3P-hydroxylation of GAZ0 to GAl in pea shoots on the basis of the following evidence: (a) Extracts from shoots of dwarf le mutants contain 10-to 18-fold less GA1 than those from the wild types (Ross et al., 1992;Smith et al., 1992); (b) the le mutation reduces the conversion of [3H]GA20 and [17-13C,3Hz]GAz0 to labeled GAl and GAs, ...

Developmental and Hormonal Regulation of Gibberellin Biosynthesis and Catabolism in Pea Fruit

“…Comparison of nearisogenic lines of pea that contain either the wild-type PsGA3ox1 gene (LELE) or a 1-bp point mutation of LE that greatly increases the K m of the encoded GA 3-oxidase (lele) demonstrated that the mutation (lele genotype) reduced GA 1 content and growth of internodes (Ross et al, 1992). The content of GA 1 was also lower (seven to 10 times) in young lele pericarps compared with those of LELE, but only minor effects on fruit growth were observed (Santes et al, 1993; MacKenzie-Hose et al, 1998). In order to determine the minimum amount of bioactive GA necessary for pea fruit set and growth, the size of the pericarp was plotted against the GA 1 concentration in nonpollinated fruit growing after application of GA 1 or GA 3 to the leaf subtending the fruit (Rodrigo et al, 1997).…”

“…Higher concentrations of GA 1 in the pericarp (20 ng g 21 fresh weight) did not result in substantial further growth. Therefore, the concentration of GA 1 in young lele pods (0.1 ng g 21 fresh weight at 6 DAA; Santes et al, 1993) may be sufficient, if not optimal, to stimulate fruit set and growth in this tissue.…”

Gibberellin 3-oxidase Gene Expression Patterns Influence Gibberellin Biosynthesis, Growth, and Development in Pea

“…Although GA 1 concentration was lower in young seeds (2.7 times) and pericarps (seven times) of lele, compared with levels in LELE at 6 d after anthesis (DAA), the growth of pods (in length) and seeds (in weight) was not affected by the le mutation. However, the levels of GA 20 and GA 29 were substantially elevated in lele compared with LELE in both tissues (Santes et al, 1993). These results suggest that 3b-hydroxylation of GA 20 to GA 1 is reduced in pericarps and seeds by the le mutation, even though it did not affect the general fruit phenotype, bringing into question a possible causal role of PsGA3ox1 (LE) in the production of GA 1 during fruit development in pea.…”

“…Santes et al (1993) investigated the effect of the le mutation on the growth and GA content of developing fruits in near-isogenic lines of pea, lines 205 + (LELE; PsGA3ox1) and 205 2 (lele). Although GA 1 concentration was lower in young seeds (2.7 times) and pericarps (seven times) of lele, compared with levels in LELE at 6 d after anthesis (DAA), the growth of pods (in length) and seeds (in weight) was not affected by the le mutation.…”

“…cell-specific expression pattern of PsGA3ox1 (LE)]. Santes et al (1993) reported that the growth of pericarp (in length) and seeds (in weight) was not affected by the le mutation; however, the effect of seed number on pericarp elongation was not investigated. We found that the BC LEle line did produce significantly longer pericarps relative to the BC lele line, but only when there was a low seed number per pericarp (three seeds; Table III).…”