ABSTRACT
Oligosaccharide synthesis is an important cryoprotection strategy used by woody plants during winter dormancy. At the onset of autumn, starch stored in the stem and buds is broken down in response to the shorter days and lower temperatures resulting in the buildup of oligosaccharides. Given that the enzyme DSP4 is necessary for diurnal starch degradation in Arabidopsis leaves, this study was designed to address the role of DSP4 in this seasonal process in Castanea sativa Mill. The expression pattern of the CsDSP4 gene in cells of the chestnut stem was found to parallel starch catabolism. In this organ, DSP4 protein levels started to rise at the start of autumn and elevated levels persisted until the onset of spring. In addition, exposure of chestnut plantlets to 4 °C induced the expression of the CsDSP4 gene. In dormant trees or cold-stressed plantlets, the CsDSP4 protein was immunolocalized both in the amyloplast stroma and nucleus of stem cells, whereas in the conditions of vegetative growth, immunofluorescence was only detected in the nucleus. The studies indicate a potential role for DSP4 in starch degradation and cold acclimation following low temperature exposure during activity-dormancy transition.
Subject(s)
Acclimatization/physiology , Fagaceae/physiology , Gene Expression Regulation, Plant/genetics , Plant Proteins/genetics , Plastids/genetics , Starch/metabolism , Cell Nucleus/metabolism , Cold Temperature , DNA, Complementary/genetics , Dual-Specificity Phosphatases/genetics , Dual-Specificity Phosphatases/metabolism , Fagaceae/genetics , Fagaceae/ultrastructure , Microscopy, Confocal , Oligosaccharides/metabolism , Photoperiod , Plant Leaves/genetics , Plant Proteins/metabolism , Plant Stems/enzymology , Plant Stems/genetics , RNA, Plant/genetics , Seasons , Seedlings/genetics , Stress, Physiological , Time Factors , Trees/enzymology , Trees/genetics , Trees/physiology , Trees/ultrastructureABSTRACT
Circadian clock performance during winter dormancy has been investigated in chestnut by using as marker genes CsTOC1 and CsLHY, which are homologous to essential components of the central circadian oscillator in Arabidopsis. During vegetative growth, mRNA levels of these two genes in chestnut seedlings and adult plants cycled daily, as expected. However, during winter dormancy, CsTOC1 and CsLHY mRNA levels were high and did not oscillate, indicating that the circadian clock was altered. A similar disruption was induced by chilling chestnut seedlings (to 4 degrees C). Normal cycling resumed when endodormant or cold-treated plants were returned to 22 degrees C. The behavior of CsTOC1 and CsLHY during a cold response reveals a relevant aspect of clock regulation not yet encountered in Arabidopsis.
