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| Authors: | N. Nii, T. Kuroiwa |
Abstract:
The cytokinin, 6-benzylamino purine (BA), was used as a foliar spray in orchard and potted plants to study its effect on branching and leaf development in peach trees, and to analyze the factors influencing its effectiveness.
Our purpose was to explore the use of BA as an aid in overcoming the problems of undesirable growth habits in peach trees.
Foliar applications of 200 ppm BA were made at 2-week intervals starting on May 1, or one week after full bloom, until the end of June during which time the shoots were actively growing.
For optimum response to BA, multiple spray applications to actively growing shoots were required.
- BA induced the buds to develop into spurs and lateral branches, while comparatively reducing the growth of the main leader (figure 1). BA significantly reduced the leaf size on the upper portion of the shoot (table 1). However, the total leaf area was larger in treated shoot because many branches had developed (figure 1). No apparent differences within the mesophyll were observed between BA and control leaves until the middle of June, at which time BA significantly reduced the anatomical development of the upper leaves on treated shoots.
Control leaves were thicker than BA-treated leaves due to the greater thickness of both the palisade and spongy parenchyma layers.
BA-treated tree were compact and many branches of BA-treated shoots contributed to a less open growth habit.
- The organization of chloroplast DNA (ctDNA) in developing and dividing peach chloroplasts was studied with the light microscope using the fluorescent probe 4'–6-diamidino-2-phenylindole(DAPI), which binds specifically to DNA (Kuroiwa and Suzuki, 1980). At the earliest stage of leaf development, during the expansion of leaf cells, the number of chloroplasts per cell and the amount of ctDNA per chloroplast increased with cell size.
BA affected chloroplast development in terms of ctDNA division (table 2). After this phase, chloroplast number per cell continued to increase, but ctDNA per chloroplast remained almost constant in both treated and untreated leaves.
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