Oxygen dynamics in submerged rice (Oryza sativa)

Area of Science:

• Plant Physiology
• Aquatic Botany
• Photosynthesis Research

Background:

• Submerged plants cannot directly exchange gases with the atmosphere.
• Underwater photosynthesis causes significant diurnal oxygen (O(2)) fluctuations.
• Previous studies indicated radial O(2) loss from rice roots after shoot illumination.

Purpose of the Study:

• To directly measure O(2) dynamics in submerged rice (Oryza sativa) shoots and roots.
• To investigate the relationship between light, O(2) levels, and tissue sugars.
• To understand the physiological basis of O(2) peaks following illumination.

Main Methods:

• Oxygen microelectrodes were used to monitor O(2) dynamics in shoots and roots.
• Measurements were taken during light and dark periods under submerged conditions.
• Tissue sugar concentrations were analyzed, with glucose added to the medium in some trials.

Main Results:

• Illumination of submerged rice shoots caused a rapid increase in O(2) (partial pressure of O(2) - pO(2)), followed by a slight decline to a quasi-steady state.
• An initial O(2) peak was observed first in shoots, then in roots, even with added glucose.
• At the quasi-steady state, shoot pO(2) was significantly higher than in darkness, improving root O(2) levels.

Conclusions:

• The initial O(2) peak in submerged rice is likely driven by high initial net photosynthesis rates, utilizing stored CO(2).
• Substrate limitation of respiration, due to declining sugars over time, may also contribute to morning O(2) peaks.
• Understanding these O(2) dynamics is crucial for submerged rice cultivation and survival.