Root growth and proton efflux rates of rice seedlings in a greenhouse environment

Marcel Giovanni Costa França,Everaldo Zonta,Roberto Oscar Pereyra Rossiello,Flávia Toledo Ramos

doi:10.1590/s0102-33062006000100003

Marcel Giovanni Costa França, Everaldo Zonta + Show 2 more

Open Access

https://doi.org/10.1590/s0102-33062006000100003

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Abstract

Growth patterns and mean proton efflux rates (E H+) in roots of rice seedlings (Oryza sativa cv. IAC 47) grown under light conditions in a greenhouse environment were studied. Fifteen days after emergence, seedlings were transferred to pots containing 3.7 L of nutrient solution with 1.43 mmol NNH4+ L¹ as the sole source of nitrogen, to induce four sequential cycles of solution acidification, starting with a pH value of 5.3. Mean proton effluxes were computed based on growth periods of 48 h (from 0 to 192 h). E H+ values were estimated from values of relative root growth rates (RGR), expressed as root area (RA) or fresh mass (FM), and the linear coefficient of the regression of total free protons in nutrient solution (U H+) on RA or FM. Total free protons in the solution and the acidification gradients (deltaU H+/deltaMF) were better related to FM than to RA. Root growth rates were affected by photosynthetic irradiance and temperature fluctuations in the greenhouse, and were not clearly related to E H+ values. However, it was concluded that when a linear relation between U H+ and fresh root mass is found, E H+ estimates expressed by FM may be more reliable than when expressed by RA units.

Highlights

Active proton (H+) efflux linked to plasma membrane H+-ATPase activity plays a central role in plant cell physiology (Michelet & Boutry 1995), taking part in metabolism and growth, through processes such as cytoplasmatic pH regulation, maintenance of turgor, cell wall relaxation and polarity rise in growing cells
The extent of the acidification was compared to variations in fresh mass and surface area of roots, in order to verify which one offers a better base for the determination of proton efflux rates
Root growth – Tab. 1 shows the variation of root area (RA), fresh mass (FM), DM and SRL values during the 192 hours of the experiment

Summary

Introduction

Active proton (H+) efflux linked to plasma membrane H+-ATPase activity plays a central role in plant cell physiology (Michelet & Boutry 1995), taking part in metabolism and growth, through processes such as cytoplasmatic pH regulation, maintenance of turgor, cell wall relaxation and polarity rise in growing cells (Serrano 1989; Stiles et al 2003; Mantelin & Touraine2004). Rates (RGR), expressed as root area (RA) or fresh mass (FM), and the linear coefficient of the regression of total free protons in nutrient solution (UH+) on RA or FM. Root growth rates were affected by photosynthetic irradiance and temperature fluctuations in the greenhouse, and were not clearly related to EH+ values.

Results

Conclusion