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  • Author or Editor: James F. Harbage x
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Anatomical events of adventitious root formation in response to root induction medium, observing changes during induction and post-induction stages, were made with microcuttings of `Gala' apples. Shoot explants on root induction medium containing water, 1.5 μm IBA, 44 mm sucrose, or 1.5 μm IBA + 44 mm sucrose after 4 days of treatment averaged 0, 0.2, 2.2, and 11.9 meristemoids per microcutting, respectively. Meristemoids formed in response to sucrose were confined to leaf gaps and traces. Time-course analysis of root induction with 1.5 μm IBA + 44 mm sucrose over 4 days revealed that some phloem parenchyma cells became densely cytoplasmic, having nuclei with prominent nucleoli within 1 day; meristematic activity in the phloem was widespread by 2 days; continued division of phloem parenchyma cells advanced into the cortex by 3 days; and that identifiable root primordia were present by 4 days. Cell division of pith, vascular cambium, and cortex did not lead to primordia formation. Meristematic activity was confined to the basal 1 mm of microcuttings. Time-course analysis of post-induction treatment revealed differentiation of distinct cell layers at the distal end of primordia by 1 day; primordia with a conical shape and several cell layers at the distal end by 2 to 3 days; roots with organized tissue systems emerging from the stem by 4 days; and numerous emerged roots by 6 days. Root initiation was detectable within 24 hours and completed by day 4 of the root induction treatment and involved only phloem parenchyma cells. Chemical names used: 1 H -indole3-butryic acid (IBA).

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The influence of root initiation medium pH on root formation was investigated in relation to uptake and metabolism of applied IBA in microcuttings of Malus ×domestica Borkh. `Gala' and `Triple Red Delicious'. Root formation and uptake of H 3-IBA were related inversely to root initiation medium pH. Maximum root count (10.3 roots) and IBA uptake were observed at pH 4.0. Regardless of pH, overall root count of `Gala' was higher (13.5 roots) than `Triple Red Delicious' (4 roots). Uptake of IBA was highest at pH 4.0 for `Gala' (1.7% uptake) and at pH 4 and 5 for `Triple Red Delicious' (0.75% uptake). Metabolism of IBA was the same regardless of root initiation medium pH or cultivar examined. One-half of the IBA taken up was converted to a compound that coeluted with IBAsp during high-performance liquid chromatography. Apparently, pH regulates root formation by affecting IBA uptake but not metabolism. The level of auxin in tissue appeared unrelated to root formation between genotypes. Chemical names used: 1H-indole-3-butyric acid (IBA); 5-H 3-indole-3-butyric acid (H 3-IBA); indole-3-butrylaspartic acid (IBAsp).

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Cold-induced changes in gene expression have been demonstrated in a number of species that vary in freezing tolerance and acclimation capacity. Relative freezing tolerance was measured based on ion leakage for both nonacclimated and acclimated S. commersonii and S. cardiophyllum parents, F1 and backcross progeny segregating for cold tolerance and acclimation capacity. Western blot analyses showed increase in a dehydrin band (47 kD)(antisera courtesy of T. Close) following cold acclimation of cold tolerant S. commersonii, and a slight increase in cold sensitive S. cardiophyllum. Expression of 47 kD cosegregated with non acclimated freezing tolerance but not with acclimated freezing tolerance. Our results show that (i) expression of dehydrins is a heritable trait in the Solanum diploid population, (ii) there is no direct relationship between relative freezing tolerance and the presence or absence of dehydrm protein following cold acclimation and (iii) based on assays measuring the residual activity of the lactate dehydrogenase (LDH) enzyme following freezing, the cryoprotective influence of `boiling stable' proteins was species dependent and is related to the freezing tolerance of the species. Supported by USDA/NRI grant 91-3700-6636 to J.P.P. and J.B.B..

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