Axillary Budbreak in a Cut Rose Crop as Influenced by Light Intensity and Red:far-red Ratio at Bud Level

When flower-bearing shoots in cut rose (Rosa ×hybrida) are harvested, a varying number of repressed axillary buds on the shoot remainder start to grow into new shoots (budbreak). Earlier experiments indicated that light reaching the bud affected the number of budbreaks. In all these studies, whole plants were illuminated with different light intensities or light spectra. The aim of this article is to disentangle the effects of light intensity and light spectrum, in this case red:far-red ratio, at the level of the buds on budbreak in a rose crop. Three experiments were conducted in which light intensity and red:far-red ratio at the level of the buds were independently varied, whereas intensity and red:far-red ratio of incident light on the crop were not changed. Light intensity and red:far-red ratio at the position of the buds were quantified and related to budbreak on the shoot remainders. Removal of vertical shoots increased light intensity and red:far-red ratio as well as budbreak (1.9 budbreaks per shoot remainder compared with 0.4 budbreaks when five vertical shoots were present). No vertical shoots and red light-absorbing shading paper over the plant base mimicked the effect of vertical shoots with respect to light intensity and red:far-red ratio, but budbreak (1.0 budbreaks) was intermediate compared with treatments with and without shoots. This suggested that the presence of shoots exerts an inhibiting effect on budbreak through both effects on light at the bud and correlative inhibition. When plants had no vertical shoots and light intensity and red:far-red ratio at bud level were changed by neutral and red light-absorbing shading paper, there was a positive effect of light intensity on budbreak (0.3 more budbreaks per shoot remainder) and no effect of red:far-red ratio. Combinations of high and low light intensity with high and low red:far-red ratio on axillary buds showed that there was a positive effect of light intensity on budbreak (0.5 more budbreaks per shoot remainder) and no effect of red:far-red ratio. Our study reveals that when light intensity and red:far-red ratio received by the plant are similar but differ at bud level, budbreak was affected by light intensity and not by red:far-red ratio.

Four Hypotheses to Explain Axillary Budbreak after Removal of Flower Shoots in a Cut-rose Crop

When flower-bearing shoots in cut-rose (Rosa ×hybrida) are harvested (removed), a varying number of repressed axillary buds on the shoot remainder start to grow into new shoots (budbreak). Besides removing within-shoot correlative inhibition, it is hypothesized that shoot removal leads to 1) increased light intensity lower in the crop canopy; 2) changes in the light spectrum (particularly red:far-red ratio); and 3) changed source:sink ratio (i.e., the ratio between supply and demand of assimilates). As a fourth hypothesis it is proposed that the degree of budbreak on a shoot remainder is also influenced by the correlative inhibition exerted by other shoots on the plant. It is the goal of this work to determine which of these four hypotheses is most important for budbreak in a cut-rose crop. Four experiments were conducted, in which these factors were varied by leaf removal, removal of mature shoots, varying the number of young shoots, shading of the crop, and application of direct light on the buds. Increase in source:sink ratio was not consistently associated with higher budbreak. If source:sink ratio was decreased by removal of leaves or a mature shoot, budbreak showed even a tendency to increase. Budbreak was subject to correlative inhibition exerted by other shoots on the plant. Treatments where more light reached the bud (as a result of less shoots, no shading of the crop, application of local light) increased budbreak. Increased red:far-red ratio had the same result as more light reaching the bud but was often interrelated with light intensity. It was concluded that after removal of the flower-bearing shoot, among the factors tested, light intensity on the buds was an important and consistent factor explaining budbreak on the shoot remainder, whereas the effect of light spectrum should be further investigated.

Combined effects of contrast between poor and rich patches and overall nitrate concentration on Arabidopsis thaliana root system structure

The law of correlative inhibition states that roots in a richer environment develop more intensively if other roots of the same plant are in a poorer environment. This probably occurs only when the cost of emitting these roots in the rich patch is compensated by the advantage of having more roots, i.e. in situations where the difference in concentration between rich and poor patches is strong or the overall nutrient amount in the environment is low. For the first time, we tested root system response to combined gradients of contrast between poor and rich patches and of overall NO3– concentration in agar gels. We set up a factorial in vitro experiment crossing contrast (null, weak, strong heterogeneity) with overall NO3– concentration (deficient, optimal, excessive). We observed an increase in ramification density with increasing heterogeneity in deficient situations; but a decrease with increasing heterogeneity in excessive situations. The interaction between overall NO3– concentration and heterogeneity had a significant effect on root ramification density and the distribution of root length in diameter classes. The overall nutrient status of the soil has to be considered to understand the effect of heterogeneity on plant development at the morphological as well as at the molecular level.

Cloning, characterization, and expression of growth regulatorCYCLIN D3-2in leafy spurge (Euphorbia esula)

We have isolated both a genomic and near full length cDNA clone for a D-class cyclin gene from the perennial weed leafy spurge. Sequence analysis indicates that this gene has the highest similarity toCYCLIN D3-2of Arabidopsis. This gene is preferentially expressed in growing shoot apices and is up-regulated in adventitious buds on resumption of growth following loss of correlative inhibition (apical dominance).CYCLIN D3-2is also induced in nongrowing adventitious buds of plants treated with gibberellic acid or after removal of leaves—treatments known to up-regulate expression of G1 to S phase transition–specific genes such asHISTONE H3in adventitious buds.CYCLIN D3-2was not induced on removal of the apical and axillary buds. Expression ofCYCLIN D3-2is down-regulated in adventitious crown buds during initiation of ecodormancy in early winter. Sequence comparisons ofCYCLIN D3-2with its putative orthologue from Arabidopsis identified several conserved motifs in the promoter region and a conserved region capable of forming a stable hairpin loop in the 5′ untranslated region. Conservation of these noncoding sequences across species strongly suggests they have a regulatory function.

Growth of first-order branches in Betula platyphylla saplings as related to the age, position, size, angle, and light availability of branches

The growth of first-order branches was measured in 25 saplings of Betula platyphylla Sukatchev var. japonica Hara growing under various light conditions in northern Hokkaido, northern Japan, and the effect of age, tip height, length, and angle of branches and light availability at the branch tips on branch growth were examined. Branch growth was evaluated as the total biomass growth of current-year long shoots within a first-order branch (TBG), the number of long shoots currently produced by the first-order branch (CSN), and the mean biomass of current-year long shoots within the first-order branch (MSG). In general, TBG, CSN, and MSG were negatively dependent on branch age and positively dependent on height, length, angle (from the horizontal), and light availability of the branch. The relationships between each of TBG, CSN, and MSG and the independent variables were individual specific. The dependency of TBG, CSN, and MSG on the light availability at the branch tips was affected by the maximum light availability at the individual level, suggesting that branch growth is affected not only by branch-level resources but also by conditions at the individual level. Based on these results, two concepts for understanding branch growth, branch autonomy and correlative inhibition, were discussed, and prediction models for TBG, CSN, and MSG were presented.