Supplementary File 4 Effect of Zn-deficiency of the photosynthetic efficiency of RIL46 and IR74
Materials and methods
An experiment was carried out in a growth chamber with an 11h dark period, a maximum light intensity of 400 µmol m-2s-1, and night temperatures of 24°C. Seeds of IR74 and RIL46 were germinated on netted Styrofoam sheets floating on 0.5 mM CaCl2, and seedlings were transferred to half strength nutrient solutions after ten days. After further ten days they were transplanted to 12 L tanks containing 0.1% agar nutrient solutions as described (Wang et al. 2008), containing either 1 µM Zn (control) or no Zn (-Zn treatment). The pH was adjusted to 5.5 and solutions were exchanged weekly.
Zinc deficiency symptoms occurred in the sensitive genotype IR74 after fifteen days of –Zn treatment. Measurements of chlorophyll fluorescence were taken from the youngest fully expanded leaf of both genotypes that emerged after the onset on visible symptoms at 17, 20 and 22 days of –Zn treatment. The measurements were made using a LICOR-6400-40 leaf chamber fluorometer (Li-Cor, Lincoln, USA).For measurements of F0 and Fm, plants were transferred to a dark room and dark adapted for one hour. The parameters Fs, F0’, and Fm’ were measured on light adapted leaves around midday. The fluorescence parameters Fv/Fm, ΦPSII, Fv’/Fm’, qP, qN, and NPQ were calculated using the nomenclature of Vankooten and Snel (1990). Data were analysed by a 3-way ANOVA, with genotype, stress treatment, and time as factors.
Results
Significant impacts of Zn-deficiency were only observed onthe parameter ΦPSII, the quantum yield efficiency of PSII. Seven days after the onset of Zn-deficiency symptoms, the ΦPSII of Zn-deficient IR74 plants was more than 20% lower than that of control plants (P<0.05) (Fig. SF4.1, left). RIL46 was able to maintain a significantly higher level of ΦPSIIunder Zn-deficiency in newly emerged leaves than inefficient IR74 (Fig. SF4.1, right).
Fig. SF4.1 The effect of Zn deficiency on the quantum yield efficiency of PSII in Zn-efficient rice line RIL46 and inefficient cultivar IR74. Measurements at day 0 were taken on older leaves; measurements on days 2-7 were taken on newly emerged leaves. Within a genotype, columns headed by the same letter are not significantly different (P>0.05). The left hand panel shows a trend towards reduced quantum yield efficiency in Zn-deficientIR74, becoming significant (P<0.05)7 days after the onset of symptoms. The right hand panel shows a similar trend in RIL46, but this effect is not statistically significant during the observation period.Note: genotype*time*treatment and genotype*treatment interactions were not significant (P>0.05), but both genotype*time and treatment*time interactions were significant (P<0.05)
References
Vankooten O, Snel JFH(1990)The use of chlorophyll fluorescense nomenclature in plant stress physiology. Photosynth Res25:147-150
Wang Y, Frei M, Wissuwa M (2008) An agar nutrient solution technique as a screening tool for tolerance to zinc deficiency and iron toxicity in rice. Soil Sci Plant Nutr54:744-750