Abstract
Some plant species develop aerenchyma to avoid anaerobic environments. In Syzygium kunstleri (King) Bahadur & R. C. Gaur, both primary and secondary aerenchyma were observed in adventitious roots under hypoxic conditions. We clarified the function of and relationship between primary and secondary aerenchyma. To understand the function of primary and secondary aerenchyma in adventitious roots, we measured changes in primary and secondary aerenchyma partial pressure of oxygen (pO2) after injecting nitrogen (N2) into the stem 0–3 cm above the water surface using Clark-type oxygen microelectrodes. Following N2 injection, a decrease in pO2 was observed in the primary aerenchyma, secondary aerenchyma, and rhizosphere. Oxygen concentration in the primary aerenchyma, secondary aerenchyma, and rhizosphere also decreased after the secondary aerenchyma was removed from near the root base. The primary and secondary aerenchyma are involved in oxygen transport, and in adventitious roots, they participate in the longitudinal movement of oxygen from the root base to root tip. As cortex collapse occurs from secondary growth, the secondary aerenchyma may support or replace the primary aerenchyma as the main oxygen transport system under hypoxic conditions.
Highlights
Flooding is a significant environmental stress for plants growing in peat-swamp forests, while periodic and constant flooding can prevent growth, yield, and distribution of plants[1,2]
The oxygen transport in primary aerenchyma of adventitious roots was confirmed by a series of p O2 measurements at different positions along the root
As a result of measuring p O2 in primary aerenchyma, we observed that the p O2 was highest in the root base and lower toward the root tip, regardless of the age of the root (Fig. 1)
Summary
Flooding is a significant environmental stress for plants growing in peat-swamp forests, while periodic and constant flooding can prevent growth, yield, and distribution of plants[1,2]. To overcome the complications caused by flooding, some plant species have a morphological escape mechanism known as low-oxygen escape syndrome, common in plant species that have adapted to prolonged flooding[10]. These phenotypic traits include the formation of aerenchyma, adventitious roots, leaf anatomical modifications, and gas pressurization by the porous tissues[10]. The movement of oxygen through the aerenchyma from the stem to the root in plants exposed to flooding conditions is very important for plant survival because it can reduce hypoxic stress. Previous studies on the aerenchyma have been focused on vegetal plants, and morphological and functional studies on aerenchyma formation of woody plants are still needed
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