Growth and development of the pod wall in spring rape (<i>Brassica napus</i>) as related to the presence of seeds and exogenous phytohormones

Abstract

SUMMARY Pod wall photosynthesis is known to contribute to nearly one-third of rape ( Brassica napus ) seed weight. The relationship between the number of seeds and the growth of the pod wall, and the effects of single and mixed applications of gibberellic acid (GA), naphthyl acetic acid (NAA) and benzyl adenine (BA) on development of the pod wall were, therefore, examined in potted plants of spring rape under glasshouse conditions. The size and weight of the pod wall were closely associated with the number of seeds per pod, and a stronger development of tissues was observed in the presence of seeds. Application of BA alone or in combination with GA (GA + BA) to emasculated flowers induced the development of parthenocarpic pods similar in size and shape to the untreated seeded pods. NAA applied singly or in mixtures produced abnormal pods. BA enhanced cell division in all tissues while GA and NAA caused expansion of parenchyma in the mesocarp. Application of BA or GA + BA at 1–5 rather than at 11–15 days after flower opening led to the development of bigger pods. Younger pods responded more than the older ones when they were treated simultaneously. BA or GA + BA application to nonemasculated flowers on the terminal raceme delayed senescence in both basal and apical pods but it increased pod size only in the latter. The balance of cytokinins and gibberellins within a pod seems to play an important role in regulating the growth of the pod wall.