Are Methanol-Derived Foliar Methyl Acetate Emissions a Tracer of Acetate-Mediated Drought Survival in Plants?

Upregulation of acetate fermentation in plants has recently been described as an evolutionarily conserved drought survival strategy, with the amount of acetate produced directly correlating to survival. However, destructive measurements are required to evaluate acetate-linked drought responses, limiting the temporal and spatial scales that can be studied. Here, 13C-labeling studies with poplar (Populus trichocarpa) branches confirmed that methyl acetate is produced in plants from the acetate-linked acetylation of methanol. Methyl acetate emissions from detached leaves were strongly stimulated during desiccation, with total emissions decreasing with the leaf developmental stage. In addition, diurnal methyl acetate emissions from whole physiologically active poplar branches increased as a function of temperature, and light-dark transitions resulted in significant emission bursts lasting several hours. During experimental drought treatments of potted poplar saplings, light-dark methyl acetate emission bursts were eliminated while strong enhancements in methyl acetate emissions lasting > 6 days were observed with their initiation coinciding with the suppression of transpiration and photosynthesis. The results suggest that methyl acetate emissions represent a novel non-invasive tracer of acetate-mediated temperature and drought survival response in plants. The findings may have important implications for the future understanding of acetate-mediated drought responses to transcription, cellular metabolism, and hormone signaling, as well as its associated changes in carbon cycling and water use from individual plants to whole ecosystems.

Effect of Leaf Age and Shading on the Phenolic Composition of Apple Foliage

Two experiments were conducted to determine the effects of leaf age and shading on the phenolic content and composition of apple foliage. In the first study, it was determined that the phenolic content of `Liberty', at increasing leaf developmental stages, was leaf age—dependent. Early during leaf development, there was an increase in the phloridzin (the primary glycoside identified) and in total phenolics, reaching a maximum when the leaf is 6 days from 20-mm blade length. After this stage, the phenolic content decreased with increasing leaf age. In the second study, the leaves of two cultivars, `Liberty' and `Starkspur Law Rome', were tagged weekly when the leaf was two-thirds unfolded. Three weeks after budbreak, the trees were placed under three shade cloth treatments (0%, 60%, and 90% shade). After 4 weeks under the shade treatments, the tagged leaves were collected to determine their phenolic content. Shade significantly affected the foliar phenolic content. Leaves in 0% shade had the highest phenolic content, whereas the lowest content was found in leaves exposed to 90% shade. There was a significant leaf age × shade interaction. The phenolic content decreased with increasing leaf age except for those leaves whose development occurred before the experiment was started. The results indicate that light and leaf developmental stage are important factors in determining the phenolic content of apple leaves, but shading appears to have a stronger influence than leaf developmental stage. E-mail [email protected]; phone (802) 656-2824.

Shading and Leaf Age Effects on Total Phenolic Content and Specific Leaf Weight of Apple

The effects of shading and leaf age on the production of foliar phenolics of two apple (Malus domestica Borkh.) cultivars, `Liberty' and `Red Rome Beauty', were studied. Potted trees were grown outdoors and their leaves tagged weekly when they reached 20 mm in length. This process continued for the duration of the experiment. At 3 weeks from budbreak, the trees were placed in three shade treatments: 0% shade (control), 60% shade, and 90% shade. After 5 weeks, the leaves were collected for phenolic assay. Specific leaf weight (SLW) was determined from the leaf below the tagged leaf. Shade significantly affected the total phenolic content. Leaves in 0% shade had the highest levels of total phenolics. The phenolic content decreased with increasing shade, with trees in 90% shade having a 72% reduction in total phenolics. There was a significant shade by leaf age interaction. There was a decrease in total phenolic content with increasing leaf age except for those leaves whose development occurred before the experiment was started. The 1-week-old leaf had the highest phenolic content, while 4-week-old leaf had the lowest amount. The 5- and 6-week-old leaves that had been tagged prior to the onset of the shade treatments has similar phenolic content in all treatment. SLW significantly decreased with increasing shade and increased with leaf age. Results of this study indicate that light and leaf developmental stage are important factors in the total foliar phenolic content, but, once phenolics are synthesized, shading does not affect their content.