Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/7/2012
Publication Date: 2/1/2013
Citation: Ratnaprabha, R., Pinson, S.R., Tarpley, L. 2013. Associating root morphology and physiology with molybdenum uptake of three rice varieties grown in three pH regimes. 35th Rice Technical Working Group Meeting Proceedings. February 27- March 1, 2012, Hot Springs, Arkansas. CDROM Interpretive Summary:
Technical Abstract: Molybdenum (Mo) is an essential micronutrient required in very low amounts (0.1-1 µg g-1 dry weight) in plants. It acts as a co-factor of certain enzymes carrying out redox reactions and is required for various physiological, biochemical and metabolic processes. However, its accumulation in excess levels in different plant parts is detrimental for plants. The accumulation patterns in different parts of the plants may be due to alterations in external-environment factors, such as acidification of the growing media, or due to changes in morphology of plant parts including roots. In 2007 and 2008, preliminary field trials in both flooded and unflooded conditions identified varieties with high Mo content in rice grains. Most of the high Mo varieties were from Malaysia, where they are likely grown in naturally acidic soils. Our hypotheses are that high seed Mo content reflects acid tolerance of those varieties and that these varieties exhibit different root morphology and physiology attributes. The objectives of this study were to 1) determine if the high-Mo varieties are adapted to high soil-solution acidity and 2) compare root morphology and physiology of high-Mo varieties with a low-Mo standard U.S. variety when grown hydroponically at different solution pH. Preliminary leaf sampling from two week-old seedlings to two month old plants showed strong association between leaf and grain Mo levels suggesting similar inter-variety accumulation patterns in different tissues. Hence, this study was conducted on 4-week old seedlings transplanted into hydroponics at 2 weeks of age. One high-Mo Malaysian variety (US core 356), one high-Mo non-Malaysian variety (US Core 823) & one low-Mo variety (Lemont) were grown in solution pHs 4.7, 5.4 and 6.1 for two weeks with six replications per run and three runs. The following parameters were measured: photosynthesis and chlorophyll (as a positive correlation exists between molybdenum-stimulated chlorophyll content and net photosynthesis rate), root exudation (as solution pH influences root exudation, which in turn influences nutrient availability and uptake) and detailed root morphology (as solution pH determines relative growth rate and thus, root morphology).