Drought causes the excessive abscission of flowers in yellow lupine, leading to yield loss and serious economic consequences in agriculture. The structure that determines the time of flower shedding is the abscission zone (AZ). Its functioning depends on the undisturbed auxin movement from the flower to the stem. However, little is known about the mechanism guiding cell–cell adhesion directly in an AZ under water deficit. Therefore, here, we seek a fuller understanding of drought-dependent reactions and check the hypothesis that water limitation in soil disturbs the natural auxin balance within the AZ and, in this way, modifies the cell wall structure, leading to flower separation. Our strategy combined microscopic, biochemical, and chromatography approaches. We show that drought affects indole-3-acetic acid (IAA) distribution and evokes cellular changes, indicating AZ activation and flower abortion. Drought action was manifested by the accumulation of proline in the AZ. Moreover, cell wall-related modifications in response to drought are associated with reorganization of methylated homogalacturonans (HG) in the AZ, and upregulation of pectin methylesterase (PME) and polygalacturonase (PG)—enzymes responsible for pectin remodeling. Another symptom of stress action is the accumulation of hemicelluloses. Our data provide new insights into cell wall remodeling events during drought-induced flower abscission, which is relevant to control plant production.

We recently showed that yellow lupine is highly sensitive to soil water deficits since this stressor disrupts nodule structure and functioning, and at the same time triggers flower separation through abscission zone (AZ) activation in the upper part of the plant. Both processes require specific transformations including cell wall remodeling. However, knowledge about the involvement of particular cell wall elements in nodulation and abscission in agronomically important, nitrogen-fixing crops, especially under stressful conditions, is still scarce. Here, we used immuno-fluorescence techniques to visualize dynamic changes in cell wall compounds taking place in the root nodules and flower AZ of Lupinus luteus following drought. The reaction of nodules and the flower AZ to drought includes the upregulation of extensins, galactans, arabinans, xylogalacturonan, and xyloglucans. Additionally, modifications in the localization of high- and low-methylated homogalacturonans and arabinogalactan proteins were detected in nodules. Collectively, we determined for the first time the drought-associated modification of cell wall components responsible for their remodeling in root nodules and the flower AZ of L. luteus. The involvement of these particular molecules and their possible interaction in response to stress is also deeply discussed herein.

Interactions among jasmonates and auxin in the photoperiodic flower induction of a short-day plant Ipomoea nil were examined. Therefore, we measured changes in jasmonic acid (JA) and jasmonic acid methyl ester (JAMe) levels in the cotyledons of I. nil during the inductive night, as well as the effects of indole-3-acetic acid (IAA) on their content. We noticed an interesting result, that IAA applied on the cotyledons of I. nil is an effective stimulator of JAMe production in seedlings cultivated under inductive night conditions. IAA treatment also significantly increased the transcriptional activity of InJMT (JASMONIC ACID CARBOXYL METHYL-TRANSFERASE), while did not affect the expression of JA biosynthesis genes (lipoxyganease, allene oxide synthase, 12-oxophytodienoate reductase). These data, as well as the results of our previous research, suggest that exogenous IAA participates in I. nil flower induction process by stimulating InJMT expression and, as a consequence of that, enhancing the level of JAMe, a flowering inhibitor.