Cell wall-bound phenolics in cells of maize (Zea mays, Gramineae) and buckwheat (Fagopyrum tataricum, Polygonaceae) with different plant regeneration abilities

Abstract

Six different tissue types were used in these studies: both regenerable and nonregenerable calli of different morphotypes of buckwheat (Fagopyrum tataricum, Polygonaceae) and maize (Zea mays, Gramineae) inbred Pa91 as well as two maize inbred cultures, H99-R and H99-NR, with similar compact (embryogenic-like) structure but different regeneration abilities. The lignin levels measured by the thioglycolic acid method in the lines with different regeneration abilities 3 weeks after subculture were somewhat higher in regenerable than in nonregenerable calli. The total amount of wall bound phenolic acids in buckwheat (dicotyledonous plant) was similar to that of maize (monocotyledonous plant), but the maize cell walls contained a much higher proportion of esterified phenolic acids than the buckwheat cell walls. The buckwheat had almost equal amounts of ester and ether linked phenolic acids, while the maize cell walls had 90% or more esterified linkages. Much higher amounts of hydroxycinnamic acids are bound to the cell walls of regenerable compared with the nonregenerable buckwheat and Pa91 calli; ferulic and p-coumaric acids in maize, and ferulic and sinapic acids in buckwheat. Room temperature alkaline treatment released almost all of the ether linked sinapic acid and about 75–80% of the total etherified ferulic acid from the buckwheat cell walls without breaking the ether linkages. The hydroxycinnamic acid contents were very similar in the two maize inbred H99 lines with similar morphology but different plant regeneration potential. These results indicate that wall bound phenolics, in particular ferulic acid, may be associated with a certain tissue morphological structure, that is necessary but not sufficient for plant regeneration since additional factors seem to be required for morphogenesis in vitro.

Introduction

The significance of cell wall biochemical and structural alternations in plant development has been emphasized recently in many reports [1], [2], [3], [4], [5], [6]. The cell wall is now considered to be a vital organelle, with a composition that can change during the cell growth cycle, during growth and development and be affected by environmental conditions and physiologically active compounds. Cell walls also contain latent regulatory molecules that can trigger and regulate developmental events. Thus the changes in cell wall metabolism needs to be investigated to understand the control of plant morphogenesis and growth.

The regulation of growth and differentiation in plants has been studied mainly in connection with alternations in cellulose [7], [8], [9] and wall matrix polysaccharides [3], [5], [10], [11], [12], [13], [14], [15], [16] with little research dedicated to the role of wall-bound phenolic compounds in plant development.

Plant cell and tissue cultures provide an experimental system for the study of cell wall involvement in the communication between different cells and tissues as well as in the growth and differentiation of cells and plant development. Usually studies of morphogenic processes in vitro are performed with callus tissues, where development is controlled by the culture medium as well as by the potential for regeneration of the callus lines. Some cultures lose their ability to regenerate plants regardless of the culture medium composition usually after an extended time in culture [5], [17], [18]. Thus regenerable and nonregenerable calli provide an appropriate experimental system to study the mechanism of morphogenesis in vitro.

Studies of the role of cell wall pectins and proteins in intracellular attachment and morphogenesis of embryogenic and nonembryogenic cultured carrot cells were carried out [5], [16], but the role of wall bound phenolics was not discussed. However, Kato et al. [19] reported that feruloyl and diferuloyl esters between polysaccharides affect aggregation in rice suspension cultures. Some phenolic acid derivatives were suggested to be regulators of cell expansion and division since they can mimic the effects of cytokinins [20], [21]. Alterations in phenolic acids, lignin and peroxidase activity were found to be related to the potential of sessile oak somatic embryos to convert into plants [22]. We have shown that regenerable tissues contain much higher levels of vanillin — presumably produced from ferulic acid by the CuSO₄–NaOH oxidation treatment of the cell walls — than nonregenerable tissues [23]. We also have reported that the differences in cell wall phenolic compounds correlate with the developmental capability of callus tissues of various species [23], [24]. These results indicate that the ferulic acid levels may be critical for calli regeneration ability.

Here we report that the total amounts of cell wall bound phenolic acids are similar in a graminaceous and a polygonaceous species, however, their linkages are quite different. Large differences were found in ferulic acid levels in the cell walls of buckwheat and maize regenerable and nonregenerable calli with typical morphological structure but not in maize with the same morphological structure.