Influence of IAA and ABA on maize stem vessel diameter and stress resistance in variable environments.

The plasticity of the xylem and its associated hydraulic properties play crucial roles in plant acclimation to environmental changes, with vessel diameter (Dv) being the most functionally prominent trait. While the effects of external environmental factors on xylem formation and Dv are not fully understood, the endogenous hormones indole-3-acetic acid (IAA) and abscisic acid (ABA) are known to play significant signalling roles under stress conditions. This study investigates how these hormones impact Dv under various environmental changes. Experiments were conducted in maize plants subjected to drought, soil salinity, and high CO2 concentration treatments. We found that drought and soil salinity significantly reduced Dv at the same stem internode, while an elevated CO2 concentration can mitigate this decrease in Dv. Remarkably, significant negative correlations were observed between Dv and the contents of IAA and ABA when considering the different treatments. Moreover, appropriate foliar application of either IAA or ABA on well-watered and stressed plants led to a decrease in Dv, while the application of corresponding inhibitors resulted in an increase in Dv. This finding underscores the causal relationship between Dv and the levels of both IAA and ABA, offering a promising approach to manipulating xylem vessel size.

Estimation of Photosynthetic Induction Is Significantly Affected by Light Environments of Local Leaves and Whole Plants in Oryza Genus.

Photosynthetic induction and stomatal kinetics are acknowledged as pivotal factors in regulating both plant growth and water use efficiency under fluctuating light conditions. However, the considerable variability in methodologies and light regimes used to assess the dynamics of photosynthesis (A) and stomatal conductance (gs) during light induction across studies poses challenges for comparison across species. Moreover, the influence of stomatal morphology on both steady-state and non-steady-state gs remains poorly understood. In this study, we show the strong impact of IRGA Chamber Illumination and Whole Plant Illumination on the photosynthetic induction of two rice species. Our findings reveal that these illuminations significantly enhance photosynthetic induction by modulating both stomatal and biochemical processes. Moreover, we observed that a higher density of smaller stomata plays a critical role in enhancing the stomatal opening and photosynthetic induction to fluctuating light conditions, although it exerts minimal influence on steady-state gs and A under constant light conditions. Therefore, future studies aiming to estimate photosynthetic induction and stomatal kinetics should consider the light environments at both the leaf and whole plant levels.

Photosynthesis of rice leaves with a parallel venation is highly tolerant to vein severing.

Vein severing in plants caused by leaf damage is common in fields where crops are cultivated. It is hypothesized that leaves with complex reticulate venation can withstand hydraulic disturbances caused by vein severing, thereby preserving leaf carbon assimilation. However, limited research focuses on vein damage of leaves with parallel venation. We studied how vein-severing affected the photosynthetic traits of rice (Oryza sativa) leaves in seconds, minutes and days, under varying water-demand conditions and differing extents of water supply disruption. Rice leaves completely lost their photosynthetic capacity within 2.5 minutes after excision. Severing the midrib resulted in reduced light-saturated photosynthetic rate (A), stomatal conductance (gsw ) and transpiration rate (E) by 2.6, 6.8 and 5.9%, respectively, already after thirty minutes. We further investigated the photosynthetic trait responses to various extents of leaf width severing, while keeping the midrib functional. Surprisingly, A, gsw and E in the downstream area of the severed leaves largely remained stable, showing minimal variation across different leaf width severing ratios. These traits declined only slightly even under increased ambient light intensity and leaf-to-air vapor pressure deficit. This sustained photosynthesis post-severing is attributed to the efficient lateral water transport. Long-term leaf damage slightly but not significantly, impacted the downstream photosynthetic traits within five days post-severing. However, a more pronounced reduction in gas exchange during leaf senescence was observed nine days after severing. These findings suggested that rice leaves can tolerate hydraulic disturbances from vein severing and maintain functionality under various conditions, which is crucial for crop yield stability. However, long-term consequences require further investigation.