Light and dark modulation of chlorophyll biosynthetic genes in response to temperature

Abstract

Temperature and light significantly influence chloroplast development and chlorophyll biosynthesis. To understand the mechanism of the modulation of chlorophyll biosynthesis, the levels of transcripts and proteins of many enzymatic steps of tetrapyrrole biosynthesis in wheat and cucumber were simultaneously examined. The effect of low (chill-stress) as well as high (heat-stress) temperatures on dark- and light-grown seedlings was monitored. The protochlorophyllide oxidoreductase (POR) content was greatly reduced in response to light in control and heat-stressed seedlings. However, the POR level was not reduced in light-exposed chill-stressed seedlings. The genes for glutamate semialdehyde aminotransferase (gsa; cucumber), glutamyl-tRNA reductase (GluTR; cucumber), 5-aminolevulinic acid dehydratase (Ala D; cucumber and wheat) and for a subunit of Mg-chelatase (Chl I; wheat) showed a reduced expression in cold stress compared to controls and heat-stress conditions. Although expression of the ferrochelatase gene (Fch) and geranylgeranyl reductase gene (Chl P) was upregulated in light, they were downregulated by both chill- and heat-stress. Interestingly, gsa and uroporphyrinogen decarboxylase gene (UroD) and gene product abundance was stimulated by light and heat-stress implying the presence of both light and heat-inducible elements in their promoters. This observation corroborates with the previous report of increased enzymatic activity of UroD in heat-stressed cucumber seedlings. The gsa and Uro D may play an important role in tolerance of the greening process of plants to heat-stress.

HSP90, ZTL, PRR5 and HY5 integrate circadian and plastid signaling pathways to regulate CBF and COR expression.

“…S2). This result is consistent with earlier reports demonstrating that the chlorophyll biosynthetic pathway is strongly inactivated and the enzymes in the pathway are inhibited by low temperatures (Mohanty et al, 2006). In contrast, CBF1 to CBF3 were strongly induced within the first 1.5 h following the shift to 4°C Figure 1.…”

Chilling tolerance of Cicer arietinum lines evaluated by photosystem II and antioxidant activities

“…Total chlorophyll contents of lines were decreased dramatically by chilling temperature, regardless of severity, particularly in AKN 290 ( Figure 1A). Mohanty et al (2006) suggested that the reason for reduced chlorophyll content in chilled cells could be decreased chlorophyll synthesis, faster chlorophyll degradation, or both. CA resulted in a significant decline in total chlorophyll content of AKN 290, but, interestingly, that reduction did not lead to any photosynthetic activity disorders as determined by chlorophyll a fluorescence measurements (Figures 2 and 3).…”

Porphyrin Biosynthesis Control under Water Stress: Sustained Porphyrin Status Correlates with Drought Tolerance in Transgenic Rice

“…During prolonged drought, HEMA1 and GSA transcript levels were down-regulated, and consequently, reduced levels of ALA and other porphyrin metabolites were found in wild-type and transgenic plants. Downregulation of the porphyrin biosynthesis genes, including GSA, HEMA, ALAD, CHLI, and FC, has also been shown in chill-stressed seedlings (Mohanty et al, 2006). Despite the disappearance of tetrapyrrole intermediates, the levels of the end product of the pathway, chlorophyll, were maintained during drought in transgenic and wild-type plants.…”