The Control of Apical Bud Growth and Senescence by Auxin and Gibberellin in Genetic Lines of Peas

Abstract

Pea (Pisum safivum L.) lines G2 (dwarf) and NCBl769 (tall) (Sn Hr) produce flowers and fruit under long (LD) or short (SD) days, but senesce only under LD. Endogenous gibberellin (CA) levels were inversely correlated with photoperiod (over 9-1 8 h) and senescence: CA,, was 3-fold and CA, was 10-to 11-fold higher in flowering SD C2 shoots, and the vegetative tissues within the SD apical bud contained 4-fold higher levels of CA,,, as compared with the LD tissues. Prefloral C2 plants under both photoperiods had CA, and CA,, levels similar to the flowering plants under LD. Levels of indole-3-acetic acid (IAA) were similar in C2 shoots in LD or SD; SD apical bud vegetative tissues had a slightly higher IAA content. Young floral buds from LD plants had twice as much IAA as under SD. In NCB1769 shoots CA, decreased after flower initiation only under LD, which correlated with the decreased growth potential. We suggest that the higher CA, content of G2 and NCB1769 plants under SD Under LD conditions fruit development in G2 pea plants results in apical senescence, but under SD conditions apical growth continues, despite the presence of a large number of fruit. This is dependent on the presence of dominant alleles at the Sn and Hr genetic loci. The photoperiodic response of G2 plants is nonphotosynthetic and quantitative, such that a brief exposure of light during the night does not reverse its SD growth habit (Proebsting et al., 1976). The growth rate of developing seeds on G2 plants is more rapid under LD than under SD conditions, which is indicative of a greater nutrient drain exerted on LD plants

Seed Production Affects Maternal Growth and Senescence in Arabidopsis

“…Furthermore, interactions with other hormones are likely to be part of correlative control, which will complicate the matter (Seth and Wareing, 1967;Zhu and Davies, 1997).…”

“…Peas seem to be a good example of such apex senescence as DNA fragmentation (a sign of cell death) was detected in mitotically arrested apices (Noodén and Penney, 2001;Wang et al, 2007). In previous work, levels of hormones such as GA and auxin were shown to be affected during monocarpic senescence in pea shoots (Leopold et al, 1959;Lindoo and Noodén, 1977;Zhu and Davies, 1997). The role and the causality of multiple correlated events during monocarpic senescence are, however, still under debate (Noodén et al, 2003;Davies and Gan, 2012).…”

Transcription Analysis of Arabidopsis Membrane Transporters and Hormone Pathways during Developmental and Induced Leaf Senescence

“…In pea (Pisum sativum), exogenous GA3 can delay apical senescence, and endogenous GA concentration is lower in senescing than in flowering shoots (Zhu and Davies, 1997). In detached Arabidopsis leaves, CK and to a lower extent GA delay chlorophyll degradation.…”

Differences in Branch Formation in Indeterminate and Determinate Tomato Types

“…Because emergence of the terminal flower bud occurred earlier than emergence of the axillary bud at the second node, the effect of the terminal flower bud on lateral shoot growth might be stronger than that on the axillary bud in both types of cultivars. Auxin is produced in the apical bud and young expanding leaves in Arabidopsis, Brussels sprouts, pea, and tomato (Tucker, 1976;Thomas, 1983;Zhu and Davis, 1997;Ljung et al, 2001). In the indeterminate cultivars, if the auxin concentration that suppresses lateral shoot elongation decreases temporarily upon ablation of the apical meristem or emergence of the terminal flower bud, the lateral shoot at the second node below the terminal flower bud elongates due to high cytokinin concentrations in the main stem.…”