Functional plant cell wall design revealed by the Raman imaging approach.

Using the Raman imaging approach, the optimization of the plant cell wall design was investigated on the micron level within different tissue types at different positions of a Phormium tenax leaf. Pectin and lignin distribution were visualized and the cellulose microfibril angle (MFA) of the cell walls was determined. A detailed analysis of the Raman spectra extracted from the selected regions, allowed a semi-quantitative comparison of the chemical composition of the investigated tissue types on the micron level. The cell corners of the parenchyma revealed almost pure pectin and the cell wall an amount of 38-49% thereof. Slight lignification was observed in the parenchyma and collenchyma in the top of the leaf and a high variability (7-44%) in the sclerenchyma. In the cell corners and in the cell wall of the sclerenchymatic fibres surrounding the vascular tissue, the highest lignification was observed, which can act as a barrier and protection of the vascular tissue. In the sclerenchyma high variable MFA (4°-40°) was detected, which was related with lignin variability. In the primary cell walls a constant high MFA (57°-58°) was found together with pectin. The different plant cell wall designs on the tissue and microlevel involve changes in chemical composition as well as cellulose microfibril alignment and are discussed and related according to the development and function.

Guard cells in albino leaf patches do not respond to photosynthetically active radiation, but are sensitive to blue light, CO2 and abscisic acid.

Stomatal openings can be stimulated by light through two signalling pathways. The first pathway is blue light specific and involves phototropins, while the second pathway mediates a response to photosynthetically active radiation (PAR). This second pathway was studied with the use of albino Vicia faba plants and variegated leaves of Chlorophytum comosum. Treatment of V. faba with norflurazon (Nf) inhibits the synthesis of carotenoids and leads to albino leaves with guard cells that lack functional green chloroplasts. Guard cells in albino leaf patches of C. comosum, however, do contain photosynthetically active chloroplasts. Stomata in albino leaf patches of both plants did not respond to red light, although blue light could still induce stomatal opening. This shows that the response to PAR is not functioning in albino leaf patches, even though guard cells of C. comosum harbour chloroplasts. Stomata of Nf-treated plants still responded to CO2 and abscisic acid (ABA). The size of Nf-treated guard cells was increased, but impalement studies with double-barrelled microelectrodes revealed no changes in ion-transport properties at the plasma membrane of guard cells. Blue light could hyperpolarize albino guard cells by triggering outward currents with peak values of 37 pA in albino plants and 51 pA in green control cells. Because of the inhibition of carotenoid biosynthesis, Nf-treated V. faba plants contained only 4% of the ABA content found in green control plants. The ABA dose dependence of anion channel activation in guard cells was shifted in these plants, causing a reduced response to 10 microM ABA. These data show that despite the dramatic changes in physiology caused by Nf, the gross responsiveness of guard cells to blue light, CO2 and ABA remains unaltered. Stomata in albino leaf patches, however, do not respond to PAR, but require photosynthetically active mesophyll cells for this response.

Cytomixis impairs meiosis and influences reproductive success in Chlorophytum comosum (Thunb) Jacq. - an additional strategy and possible implications.

Spontaneous intercellular chromatin migration/cytomixis was observed to occur in the pollen mother cells (PMCs) of the Chlorophytum comosum for the first time. The migration through cytomictic channels was more pronounced in meiosis-I and very rare in meiosis-II. The process was associated with erratic meiosis, which was characterized by defects in chromosome organization and segregation. Cytomixis was more intense in the month of April than in July and consequently the frequency of meiotic irregularities was much more pronounced during the month of April. As a consequence of abnormal meiosis, fertility was drastically reduced resulting in meager seed efficiency of 17% only. Recombination system also does not guarantee the release of sufficient variability. We view the phenomenon of cytomixis as genetically controlled mechanism involving meiotic genes and operating through signal transduction pathway triggered by the environmental stimuli. The evolutionary significance and tenable hypothesis in the backdrop of existing literature is also proposed.