Two maize inbred lines, the foundation genotype Y478 and its derived line Z58, are widely used to breed novel maize cultivars in China, but little is known about which traits confer Z58 with superior drought tolerance and yield. In the present study, responses in growth traits, photosynthetic parameters, chlorophyll fluorescence and leaf micromorphological characteristics were evaluated in Y478 and Z58 subjected to water-deficit stress induced by PEG 6000. The derived line Z58 showed greater drought tolerance than Y478, which was associated with higher leaf relative water content (RWC), root efficiency, and strong growth recovery. Z58 showed a higher stomatal density and stomatal area under the non-stressed condition; in these traits, both genotypes showed a similar decreasing trend with increased severity of water-deficit stress. In addition, the stomatal size of Y478 declined significantly. These micromorphological differences between the two lines were consistent with changes in physiological parameters, which may contribute to the enhanced capability for growth recovery in Z58. A non-linear response of Fv/Fm to leaf RWC was observed, and Fv/Fm decreased rapidly with a further gradual decline of leaf RWC. The relationship between other chlorophyll fluorescence parameters (photochemical quenching and electron transport rate) and RWC is also discussed.
 Lizana, C., Wentworth, M., Martinez, J.P., Villegas, D., Meneses, R., et al. (2006) Differential adaptation of two varieties of common bean to abiotic stress. Effects of drought on yield and photosynthesis. Journal of Experimental Botany, 57, 685-697. doi:10.1093/jxb/erj062
 Fan, X.W., Li, F.M., Song, L., Xiong, Y.C., An, L.Z., Jia, Y. and Fang, X.W. (2009) Defense strategy of old and modern spring wheat varieties during soil drying. Physiologia Plantarum, 136, 310-23. doi:10.1111/j.1399-3054.2009.01225.x
 Liang, J.S. and Zhang, J.H. (1999) The relations of stomatal closure and reopening to xylem ABA concentration and leaf water potential during soil drying and rewatering. Plant Growth Regulation, 29, 77-86. doi:10.1023/A:1006207900619
 Li, Y.Z., Sun, C.B., Huang, Z.B., Pan, J.L., Wang, L. and Fan, X.W. (2009) Mechanisms of progressive water deficit tolerance and growth recovery of Chinese maizes foundation genotypes of Huangzao 4 and Chang7-2, which are proposed on the basis of comparison of physiological and transcriptomic responses. Plant and Cell Physiology, 50, 1-20. doi:10.1093/pcp/pcp145
 Chaves, M.M., Flexas, J. and Pinheiro, C. (2009) Photosynthesis under drought and salt stress: Regulation mechanisms from whole plant to cell. Annals of Botany, 103, 551-560. doi:10.1093/aob/mcn125
 Hayano-Kanashiro, C., Calderón-Vázquez, C., IbarraLaclette, E., Herrera-Estrella, L. and Simpson, J. (2009) Analysis of gene expression and physiological responses in three Mexican maize landraces under drought stress and recovery irrigation. PLoS One, 4, e7531. doi:10.1371/journal.pone.0007531
 Fan, X.W., Li, F.M., Xiong, Y.C., An, L.Z. and Long, R.J. (2008) The cooperative relation between non-hydraulic root signals and osmotic adjustment under water stress improves grain formation for spring wheat varieties. Physiologia Plantarum, 132, 283-292. doi:10.1111/j.1399-3054.2007.01007.x
 Changhai, S., Baodi, D., Yunzhou, Q., Yuxin, L., Lei, S., Mengyu, L. and Haipei, L. (2010) Physiological regulation of high transpiration efficiency in winter wheat under drought conditions. Plant Soil Environment, 56, 340-347
 Pingali, P.L. and Pandey, S. (2001) Meeting world maize needs: Technological opportunities and priorities for the public sector. CIMMYT 1999-2000 World Maize Facts and Trends Meeting World Maize Needs Technological Opportunities and Priorities for the Public Sector 2001.
 Wang, Z.Y., Li, F.M., Xiong, Y.C. and Xu, B.C. (2008) Soil-water threshold range of chemical signals and drought tolerance was mediated by ROS homeostasis in winter wheat during progressive soil drying. Journal of Plant Growth Regulation, 27, 309-319. doi:10.1007/s00344-008-9057-4
 Abbruzzese, G., Beritognolo, I., Muleo, R., Piazzai, M., Sabatti, M., Mugnozza, G.S. and Kuzminsky, E. (2009) Leaf morphological plasticity and stomatal conductance in three Populus alba L. genotypes subjected to salt stress. Environmental and Experimental Botany, 66, 381-388. doi:10.1016/j.envexpbot.2009.04.008
 Lawlor, D.W. and Cornic, G. (2002) Photosynthetic carbon assimilation and associated metabolism in relation to water deficits in higher plants. Plant Cell and Environment, 25, 275-294. doi:10.1046/j.0016-8025.2001.00814.x
 Lafitte, R. (2002) Relationship between leaf relative water content during reproductive stage water deficit and grain formation in rice. Field Crops Research, 76, 165-174. doi:10.1016/S0378-4290(02)00037-0
 Nautiyal, P.C., Rachaputi, N.R. and Joshi, Y.C. (2002) Moisture deficit-induced changes in leaf-water content, leaf carbon exchange rate and biomass production in groundnut cultivars differing in specific leaf area. Field Crops Research, 74, 67-79. doi:10.1016/S0378-4290(01)00199-X
 Yoo, C.Y., Pence, H.E., Hasegawa, P.M. and Mickelbart, M.V. (2009) Regulation of transpiration to improve crop water use. Critical Reviews in Plant Sciences, 28, 410-431. doi:10.1080/07352680903173175
 Meng, L., Li, L., Chen, W., Xu, Z. and Liu, L. (1999) Effect of water stress on stomatal density, length, width and net photosynthetic rate in rice leaves. Journal of Shenyang Agricultural University, 30, 477-480.
 Xu, Z.Z. and Zhou, G.S. (2008) Responses of leaf stomatal density to water status and its relationship with photosynthesis in a grass. Journal of Experimental Botany, 59, 3317-3325. doi:10.1093/jxb/ern185
 Souza, R.P., Machado, E.C., Silva, J.A.B., Lagoa, A.M.M.A. and Silveira, J.A.G. (2004) Photosynthetic gas exchange, chlorophyll fluorescence and some associated metabolic changes in cowpea (Vigna unguiculata) during water stress and recovery. Environmental and Experimental Botany, 51, 45-56. doi:10.1016/S0098-8472(03)00059-5
 Conroy, J.P., Smillie, R.M., Kuppers, M., Bevege, D.I. and Barlow, E.W. (1986) Chlorophyll a fluorescence and photosynthetic and growth responses of Pinus radiata to phosphorus deficiency, drought stress, and high CO2. Plant Physiology, 81, 423-429.
 Woo, N.S., Badger, M.R. and Pogson, B.J. (2008) A rapid, non-invasive procedure for quantitative assessment of drought survival using chlorophyll fluorescence. Plant Methods, 4, 27. doi:10.2307/2444243
 Araus, J.L., Alegre, L., Tapia, L., Calafell, R. and Serret, M.D. (1986) Relationship between photosynthetic capacity and leaf structure in several shade plants. American Journal of Botany, 73, 1760-1770. doi:10.1093/jxb/erg087
 Schluter, U., Muschak, M., Berger, D. and Altmann, T. 2003. Photosynthetic performance of an Arabidopsis mutant with elevated stomatal density (sdd1-1) under different light regimes. Journal of Experimental Botany, 54, 867-874.