Fe toxicity tolerance is advantageous in rice growth recovery after Fe stress alleviation

Background
Fe toxicity often inhibits rice growth on acid sulfate soils in tropical coastal lowlands. Previous studies in plant physiology and breeding have focused on high-Fe stress, but not on growth recovery after stress alleviation.

Aims
The objective of this study was to elucidate the morphophysiological characteristics in rice growth recovery from high-Fe stress.

Methods
We evaluated the seedling growths of Taichung65 (T65) (Fe toxicity-tolerant) and Ciherang (susceptible) in hydroponic culture, during the period of high-Fe stress (250 mg Fe2+ L−1 for 12 or 18 days) and after stress alleviation.

Results
The plant growth rate during recovery was negatively correlated with the leaf bronzing score (damage symptoms due to Fe toxicity) at the end of high-Fe stress, which in turn was negatively correlated with the shoot Fe concentration. After 18-day stress, T65 showed greater growth recovery than Ciherang, attributable to its higher net assimilation rate, higher transpiration rate (water uptake/green leaf area), and greater increase in total root length during recovery. In particular, T65 showed vigorous lateral root development in nodal roots that emerged during the stress period and vigorous growth of nodal roots that emerged during recovery.

Conclusions
Our results suggest that tolerance to high-Fe stress confers an advantage in growth recovery. It is likely that tolerance to Fe toxicity contributes not only to the maintenance of green leaf area at the end of stress but also to quick root growth recovery, leading to vigorous water uptake and high photoassimilation capacity after stress alleviation.