Floral Activity in Solutions of Deoxyribonucleic Acid Extracted from Tobacco Stems

Abstract

The transition of a flowering plant from vegetative to reproductive growth is preceded presumably by biochemical changes within the shoot apex that render the apex capable of forming flowers instead of leaves. Any apex which has attained a flowering capability is considered to be in a floral state. Recently, several investigators (3,8,9,14,18,19,22,23,25,26,31) utilizing segments cut from floral branches or cut from along the stem axes in the inflorescences of flowering plants have shown that these segments, like floral-induced apices, initiate flowers instead of leaves. Thus, the in vivo inductive attainment of a floral state by plant tissues can be extended below the apex into the stem.The floral state in stems has been studied most thoroughly for cv. Wis. 38 tobacco plants. In this cv., Aghion-Prat (1, 2) found that in the internodes along the stem axis of a flowering plant that was an inhibitor gradient in flower bud formation (the floral gradient), and Wardell and Skoog (32) found that the inhibitor gradient in flower bud formation occurred simultaneously with a promotive gradient in vegetative bud formation. The floral gradient, therefore, was a gradient change in bud expression rather than a gradient decrease in the over-all capacity to form buds. Wardell and Skoog (31) showed that segments cut from the top of a flowering plant (intemodes 1-4) and treated with The extent to which the floral gradient may be due to an inverse gradient in endogenous IAA has been investigated (25, 32) by completely counteracting with RNA base analogs the inhibitory action of IAA on floral expression. As expected, below-gradient segments treated with base analogs increased (8-fold) in their floral expression to the extent that they became identical in bud expression to top segments not treated with base analogs. However, the floral expression of top segments treated with base analogs also increased (3-fold). And the floral expression of base analog-treated segments cut from along the region of the stem corresponding to the floral gradient all increased so that the floral gradient remained. On these bases, Wardell and Skoog have suggested that some factor, besides IAA, with a gradient distribution, also is involved in the regulation of floral expression.Another gradient factor correlated with floral expression of tobacco stem segments has been reported (33). Using methodology developed specifically for extracting DNA from tobacco stems already in a floral state, it has been found that a gradient in DNA roughly paralleled the floral gradient, and that the low concentrations of IAA effective in inhibiting floral expression also inhibited thymidine incorporation into DNA. In striking contrast, low concentrations of IAA promoted thymidine incorporation into DNA in stem sections cut from young vegetative plants. Leaves

Floral Induction of Vegetative Plants Supplied a Purified Fraction of Deoxyribonucleic Acid from Stems of Flowering Plants

“…Figure 10 shows that no significant amount of denatured DNA (heavy shoulder) is present. Comparative results can be seen in Figure 7, b and e. Finally, the purified rapidly renatured DNA has been tested for floral activity by the procedure already used to demonstrate floral activity in heated-cooled DNA solution (18). The results are presented in Table II.…”

“…Taking all these results together, it has been suggested that the opposite effects of IAA on both DNA synthesis and bud expression may be connected. On this basis, it has been proposed that stem segments of vegetative and flowering plants may differ in their DNA make- been reported (18). It has been shown that solutions containing DNA from stems of flowering plants effect flowering of vegetative plants, and solutions containing DNA from stems of vegetative plants are ineffective.…”

“…To gain some insight into the nature of that substance, the requirement for intact DNA has been tested (18). By mixing a solution containing DNA from stems of flowering plants with DNase I, it has been demonstrated that the enzyme chops the DNA into small fragments and that a heated-cooled solution containing these fragments can no longer effect flowering.…”

“…In Figure 8 The studies on in vitro bud expression in stems of vegetative and flowering tobacco plants (19,20) now can be extended to include the large difference in rapidly renaturing DNA. As the next step, rapidly renatured DNA has been purified from heated-cooled DNA solution and has been tested (18) to determine if it is a flower-inducing substance.…”