Changes in size and composition of pigweed (Amaranthus hybridus L.) calcium oxalate crystals under CO starvation conditions.

The functional role(s) of plant calcium oxalate (CaOx) crystals are still poorly understood. Recently, it was shown that crystals function as dynamic carbon pools whose decomposition could provide CO to photosynthesis when stomata are closed (e.g. under drought conditions) and CO starvation conditions may be created within the mesophyll. This biochemical process, named as 'alarm photosynthesis', can become crucial for plant survival under adverse conditions. Here, we study crystal decomposition under controlled CO starvation conditions (either in the shoot or in the root) to obtain a better insight into the process of crystal formation and function. Hydroponically grown pigweed plants were kept in CO -free air and/or CO -free nutrient medium for 9 days. Crystal volume was monitored daily, and carbon stable isotope composition (δ C) and Fourier transformation Raman spectra were obtained at the end of the experiment. A considerable reduction in the leaf crystal volume was observed in shoot-CO -starved plants at the end of the experiment. The smallest crystals were isolated from the plants in which carbon was excluded from both the shoot and the root and contained potassium nitrate. Crystal δ C of CO -starved plants was altered in a predicted way. Specifically, it depended on the average calculated isotope fractionation of all carbon fixation processes considered to be contributing in each experimental treatment. The results of the present study confirmed the correlation between CO starvation conditions and the CaOx crystal decomposition. Inorganic carbon fixed in the root may represent a major carbon source for CaOx formation.

© 2018 Scandinavian Plant Physiology Society.