[WHOLE PLANT AND ECOPHYSIOLOGY] A Diurnal Component to the Variation in Sieve Tube Amino Acid Content in Wheat

2008-06-04

We have used high-sensitivity capillary electrophoresis coupled to a laser-induced fluorescence detection method to quantify 16 amino acids in wheat (Triticum aestivum) sieve tube (ST) samples as small as 2 nL collected by severing the stylets of feeding aphids. The sensitivity of the method was sufficient to determine a quantitative amino acid profile of individual STs without the need to bulk samples to produce larger volumes for analysis. This allowed the observation of the full range of variation that exists in individual STs. Some of the total concentrations of amino acids recorded are higher than those reported previously. The results obtained show variation in the concentrations of phenylalanine (Phe), histidine/valine (His/Val), leucine/isoleucine (Leu/Ile), arginine, asparagine, glutamine, tyrosine (Tyr), and lysine (Lys) across the ST samples. These could not be explained by plant-to-plant variation. Statistical analyses revealed five analytes (Tyr, Lys, Phe, His/Val, and Leu/Ile) that showed striking covariation in their concentrations across ST samples. A regression analysis revealed a significant relationship between the concentrations of Tyr, Lys, Phe, Leu/Ile, His/Val, asparagine, arginine, and proline and the time of collection of ST samples, with these amino acids increasing in concentration during the afternoon. This increase was confirmed to occur in individual STs by analyzing samples obtained from stylet bundles exuding for many hours. Finally, an apparent relationship between the exudation rate of ST sap and its total amino acid concentration was observed: samples containing higher total amino acid concentrations were observed to exude from the severed stylet bundles more slowly.

[WHOLE PLANT AND ECOPHYSIOLOGY] The Stomata of the Fern Adiantum capillus-veneris Do Not Respond to CO2 in the Dark and Open by Photosynthesis in Guard Cells

Doi, M., Shimazaki, K.-i. — 2008-06-04

The stomata of the fern Adiantum capillus-veneris lack a blue light-specific opening response but open in response to red light. We investigated this light response of Adiantum stomata and found that the light wavelength dependence of stomatal opening matched that of photosynthesis. The simultaneous application of red (2 µmol m^–2 s^–1) and far-red (50 µmol m^–2 s^–1) light synergistically induced stomatal opening, but application of only one of these wavelengths was ineffective. Adiantum stomata did not respond to CO₂ in the dark; the stomata neither opened under a low intercellular CO₂ concentration nor closed under high intercellular CO₂ concentration. Stomata in Arabidopsis (Arabidopsis thaliana), which were used as a control, showed clear sensitivity to CO₂. In Adiantum, stomatal conductance showed much higher light sensitivity when the light was applied to the lower leaf surface, where stomata exist, than when it was applied to the upper surface. This suggests that guard cells likely sensed the light required for stomatal opening. In the epidermal fragments, red light induced both stomatal opening and K⁺ accumulation in guard cells, and both of these responses were inhibited by a photosynthetic inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea. The stomatal opening was completely inhibited by CsCl, a K⁺ channel blocker. In intact fern leaves, red light-induced stomatal opening was also suppressed by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. These results indicate that Adiantum stomata lack sensitivity to CO₂ in the dark and that stomatal opening is driven by photosynthetic electron transport in guard cell chloroplasts, probably via K⁺ uptake.

PLANT PHYSIOLOGY WHOLE PLANT AND ECOPHYSIOLOGY

[WHOLE PLANT AND ECOPHYSIOLOGY] A Diurnal Component to the Variation in Sieve Tube Amino Acid Content in Wheat

[WHOLE PLANT AND ECOPHYSIOLOGY] The Stomata of the Fern Adiantum capillus-veneris Do Not Respond to CO2 in the Dark and Open by Photosynthesis in Guard Cells