Variation in vein density and mesophyll cell architecture in a rice deletion mutant population

Abstract

There is a need to develop rice plants with improved photosynthetic capacity and efficiency in order to enhance potential grain yield. Alterations in internal leaf morphology may be needed to underpin some of these improvements. One target is the production of a ‘Kranz-like’ anatomy, commonly considered to be required to achieve the desired levels of photosynthesis seen in C4 crops. Kranz anatomy typically has two or three mesophyll cells interspersing adjacent veins. As a first step to determining the potential for such anatomical modifications in rice leaves, a population of rice deletion mutants was analysed for alterations in vein patterning and mesophyll cells in the interveinal regions. Significant variation is demonstrated in vein arrangement and the sequential distribution of major and minor veins across the leaf width, although there is a significant correlation between the total number of veins present and the width of the leaf. Thus the potential is demonstrated for modifying rice leaf structure. Six distinct rice mutant lines, termed altered leaf morphology (alm) mutants, were analysed for the architecture of their interveinal mesophyll cell arrangement. It is shown that in these mutant lines, the distance between adjacent minor veins and adjacent minor and major veins is essentially determined by the size of the interveinal mesophyll cells rather than changes in mesophyll cell number across this region, and hence interveinal distance changes as a result of cell expansion rather than cell division. This observation will be important when developing screens for traits relevant for the introduction of Kranz anatomy into rice.This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited.This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

The Evolutionary Basis of Naturally Diverse Rice Leaves Anatomy

“…It has been reported earlier that an increase in vein number per unit area in rice leaves was due to a change in vein diameter or due to the reduced size of other cells as an immediate compensatory mechanism [20, 61]. Here we demonstrate that the increase in vein number in Oryza can also be due to an actual change in the number of mesophyll cells rather than just having a change in cell size (S4 Table).…”

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A natural variant of NAL1, selected in high-yield rice breeding programs, pleiotropically increases photosynthesis rate

“…The functional allele of ERECTA reduced stomatal density and thereby lowered stomatal conductance relative to loss-of-function alleles; for this reason, ERECTA is regarded as a transpiration efficiency gene. Recently, rice mutants generated by artificial mutagens were screened for mesophyll cell architecture with the goal of improving photosynthetic capacity47. Several mutant lines showed favourable alterations such as increased mesophyll cell size.…”

Influence of leaf vein density and thickness on hydraulic conductance and photosynthesis in rice (Oryza sativa L.) during water stress

“…Mesophyll cells are more numerous in C 3 than C 4 plants, which increases IVD in C 3 plants7072 and reduces their K leaf 2343. Smillie et al 73 reported that IVD of rice plants is more dependent on cell size than cell number, which suggests that the lower IVD under water deficit conditions is mostly a result of more tightly packed, small mesophyll cells. The tightly packed mesophyll cells in smaller leaves under water deficit (Table 2) would produce more resistance in the apoplastic pathway for water transport in leaves, which would decrease K leaf and the subsequent K plant .…”

“…Rice leaf veins were divided into three categories based on their size (i.e., midrib, major and minor veins) to calculate the leaf vein density73. One centimeter leaf sections were excised with a razor blade from the middle portion of newly-developed leaves after measuring the leaf width.…”