Effects of NO3 – Availability on Total Productivity, Root Morphology, Photosynthesis and Nitrogen Metabolism of Lettuce (Lactuca sativa L.) Recombinant Inbred Lines

J He,L Qin,S.-F Goh

doi:10.2174/1874294701408010024

Abstract

We have identified certain heat-resistant (HR) and heat-sensitive (HS) lettuce (Lactuca sativa) recombinant inbred lines (RILs) from 113 lines under hot ambient temperature by studying the root morphology, shoot and root productivity. Except for temperature, one of the other major determinants of root morphology is nitrate (NO3-) availability. In this study, total productivity, root morphology, photosynthesis and nitrogen (N) metabolism of two RILs, 168 HS and 200 HR were studied under full N (100% NO3-), +N (125% NO3-) and –N (50% NO3-). The shoot and root productivity of both RILs under +N and –N treatments declined compared to those of full N plants. Reductions in root length, root surface area and total number of root tips were observed in 168 HS plants under both +N and –N treatments. For 200 HR plants, they all had similar values of root parameters regardless of N treatments. There were no significant differences in the light saturated CO2 assimilation (Asat) and stomatal conductance (gs sat) between two RIL plants For each lettuce RIL, no differences in total chlorophyll (Chl ) content and Chl a/b ratio were observed among the different N treatment. For both lettuce RILs, shoot NO3- concentration was highest in +N followed by full N plants and –N plants had the lowest values. There were no differences in root NO3- concentration between +N and full N plants but root NO3- concentration was significantly lower in –N plants than in +N and full N plants. For shoot total reduced N, +N plants had significantly higher concentration in both RILs compared to those of full N and –N plants. All plants had similar root total reduced N concentrations except for 168 HS under –N condition, which had significantly lower total reduced N concentrations. Differences in shoot maximal nitrate reductase (NR) activity among the different N treated plants were similar to those of total reduced N concentration. The relationships among NO3- availability, root morphology, productivity, photosynthesis and N metabolism were discussed.

Highlights

Nitrogen (N) is one of the most important minerals required for plant growth
Figs. (1E and 1F) show that shoot/root Fresh Weight (FW) ratio was higher in both recombinant inbred lines (RILs) grown under +N compared to full N and –N treatments
It was surprise to see that increase the supply of NO3– (+N plants) resulted in the decreases of shoot and root productivity in both lettuce RILs (Figs. 1A to 1D) there was no change in photosynthetic gas exchange (Fig. 3) compared to those of full N plants

Summary

Introduction

Nitrogen (N) is one of the most important minerals required for plant growth. The major N source in soil is nitrate (NO3–). Studies have shown that NO3– availability in the soil affects shoot and root production and root morphology [5, 6]. The initiation and elongation of Arabidopsis lateral root development is stimulated by local availability of NO3– [7]. It was reported that birch (Betula pendula) plants allocate relatively less nutrients to the roots when NO3– is highly available in the soil [10]. These results indicate that the N uptake and assimilation is greatly promoted by increasing C supply

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Discussion

Conclusion