Anoxia-induced elevation of cytosolic Ca2+ concentration depends on different Ca2+ sources in rice and wheat protoplasts

Abstract

The anoxia-dependent elevation of cytosolic Ca(2+) concentration, [Ca(2+)](cyt), was investigated in plants differing in tolerance to hypoxia. The [Ca(2+)](cyt) was measured by fluorescence microscopy in single protoplasts loaded with the calcium-fluoroprobe Fura 2-AM. Imposition of anoxia led to a fast (within 3 min) significant elevation of [Ca(2+)](cyt) in rice leaf protoplasts. A tenfold drop in the external Ca(2+) concentration (to 0.1 mM) resulted in considerable decrease of the [Ca(2+)](cyt) shift. Rice root protoplasts reacted upon anoxia with higher amplitude. Addition of plasma membrane (verapamil, La(3+) and EGTA) and intracellular membrane Ca(2+)-channel antagonists (Li(+), ruthenium red and cyclosporine A) reduced the anoxic Ca(2+)-accumulation in rice. Wheat protoplasts responded to anoxia by smaller changes of [Ca(2+)](cyt). In wheat leaf protoplasts, the amplitude of the Ca(2+)-shift little depended on the external level of Ca(2+). Wheat root protoplasts were characterized by a small shift of [Ca(2+)](cyt) under anoxia. Plasmalemma Ca(2+)-channel blockers had little effect on the elevation of cytosolic Ca(2+) in wheat protoplasts. Intact rice seedlings absorbed Ca(2+) from the external medium under anoxic treatment. On the contrary, wheat seedlings were characterized by leakage of Ca(2+). Verapamil abolished the Ca(2+) influx in rice roots and Ca(2+) efflux from wheat roots. Anoxia-induced [Ca(2+)](cyt) elevation was high particularly in rice, a hypoxia-tolerant species. In conclusion, both external and internal Ca(2+) stores are important for anoxic [Ca(2+)](cyt) elevation in rice, whereas the hypoxia-intolerant wheat does not require external sources for [Ca(2+)](cyt) rise. Leaf and root protoplasts similarly responded to anoxia, independent of their organ origin.

Calcium-Mediated Abiotic Stress Signaling in Roots

“…For example, when challenged by anoxia, root protoplasts from hypoxia-tolerant rice display a greater [Ca 2+ ] cyt signature than hypoxia-intolerant wheat root protoplasts (Yemelyanov et al, 2011). The location of the Ca 2+ influx also varies; use of pharmacological blockers showed that the rice signature was generated by both PM influx and store release whilst wheat appeared to rely solely on stores (Yemelyanov et al, 2011). The types of Ca 2+ channels mediating the [Ca 2+ ] cyt increase have yet to be identified in any species.…”

Mitochondrial Energy Signaling and Its Role in the Low-Oxygen Stress Response of Plants

“…Ca 2+ release from mitochondria may rather represent a hallmark of cellular energy crisis and loss of homeostasis than contribute to a specific signal. Yet, the cytosolic increase in Ca 2+ that has been consistently observed at hypoxia appears to be conserved throughout plants and chemical suppression hampers transcriptional induction of hypoxia-responsive genes such as ALCOHOL DEHYDROGENASE (Subbaiah et al, 1994;Sedbrook et al, 1996;Yemelyanov et al, 2011). The mechanism by which Ca 2+ fluxes modulate nuclear transcription is currently unknown.…”

The effect of exogenous calcium on cucumber fruit quality, photosynthesis, chlorophyll fluorescence, and fast chlorophyll fluorescence during the fruiting period under hypoxic stress

“…The involvement of calcium in hypoxia responses has been observed in many plants such as rice, wheat, and cucumber [10, 11]. This hypoxia-mediated elevation of Ca 2+ is fundamental for the activation of genes and synthesis of proteins required for acclimation responses at the cellular, tissue, and organismal levels [6, 12].…”