Diffusible and Extractable Growth Regulators in Normal and Dwarf Shoot Apices of Peach, Prunus persica Batsch

Abstract

Brian and Hemming (1), upon educing genetic dwarfs to behave as normal plants by applications of gibberellic acid, proposed that dwarfism was hormonally regulated. Phinney and his co-workers (12) expanded this idea by proposing that dwarfism in corn (Zea mays) is controlled by nonallelic genes, each of which governs a different step in gibberellin biosynthesis. They found that in this species the dwarf character, when transmitted as a recessive factor, can be altered by successive application of GA so that the seedling develops, flowers, and fruits as a normal plant. However, seedlings which inherit the dwarfing character as a dominant factor do not respond to GA treatments. Similarly, dwarf peas (Pisum sativum) respond to GA applications but the normal seedlings do not (2, 8). In rice (Oryza sativa), both the dwarf and semidwarf cultivars respond to exogenous GA. In contrast to the above species, applications of GA to normal peach (Prunus persica) seedlings accelerate shoot growth and inhibit flower bud formation (3), whilt the same treatments to dwarf progenies evoke a meager growth response. Moreover, the dwarf character in this species is transmitted as a simple recessive Mendelian factor; hence, it is likely determined by an allele and a single gene. It appears that while the genetic heritability of dwarfism in peach is simple, the mechanism controlling this character is dissimilar to that of other sp:cies mentioned above. To explore this dwarfing mechanism in peach, the levels of free diffusible and extractable gibberellin-like substances, IAA and ABA, in the shoot apices of dwarf and normal seedlings were compared.