John N. Nishio

Leaves and light capture: Light propagation and gradients of carbon fixation within leaves

The optical properties of leaves are remarkable: leaf epidermal cells commonly focus light; palisade cells channel light; and the intercellular air spaces intensely scatter light, which increases the probability for absorption for photosynthesis. New and sophisticated experimental techniques now make it possible to study how light behaves within the cell layers of a leaf and to measure internal gradients in photo-synthetic capacity. Thus, it is now possible to examine how variations in leaf anatomy can maximize photosynthetic performance in a wide variety of species and habitats.

Carbon Fixation Gradients across Spinach Leaves Do Not Follow Internal Light Gradients.

In situ measurements of 14C-CO2 incorporation into 40-[mu]m paradermal leaf sections of sun- and shade-grown spinach leaves were determined. Chlorophyll, carotenoid, and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content in similar 40-[mu]m paradermal leaf sections was also measured. The carbon fixation gradient did not follow the leaf internal light gradient, which decreases exponentially across the leaf. Instead, the 14C-CO2 fixation was higher in the middle of the leaf. Contrary to expectations, the distribution of carbon fixation across the leaf showed that the spongy mesophyll contributes significantly to the total carbon reduced. Approximately 60% of the carboxylation occurred in the palisade mesophyll and 40% occurred in the spongy mesophyll. Carbon reduction correlated well with Rubisco content, and no correlation between chlorophyll and carotenoid content and Rubisco was observed in sun plants. The correlation among chlorophyll, carotenoids, Rubisco, and carbon fixation was higher in shade leaves than in sun leaves. The results are discussed in relation to leaf photosynthetic and biochemical measurements that generally consider the leaf as a single homogeneous unit.

Iron deficiency studies of sugar beet using an improved sodium bicarbonate‐buffered hydroponic growth system

Abstract A sodium bicarbonate (NaHCO3)‐buffered hydroponic growth system was developed that simulates alkaline soil growth conditions necessary to screen sugar beet genotypes for iron (Fe) efficiency character. Three genotypes (NB1, NB4, and F, hybrid, NB 1xNB4) with differing capacities for Strategy I Fe responses were phenotyped successfully using this system. Genotypes NB1 and NB1xNB4 are Fe efficient, while NB4 is Fe inefficient. It was demonstrated that 5 mM NaHCO3 provided buffering within an optimal range (pH 7.3 ‐ pH 6.3) for the duration of ‐Fe treatments, promoted enhanced H+ extrusion, and increased the in vivo capacity for Fe3+‐chelate reduction (Fe3+‐chelate reductase [FCR] activity), especially in the roots of the Fe efficient genotypes. The same concentrations of NaHCO3 did not interfere with Fe supply to +Fe control plants of any genotype. The in vivo capacity for Fe3+‐chelate reduction increased over fivefold in both Fe efficient genotypes (NB1 and NB 1xNB4), but just under twofold in the Fe inefficient genotype (NB4). Localization and duration of enhanced Fe3+‐chelate reduction capacity were dependent upon the Fe efficiency character of each genotype.

Early Iron Deficiency Stress Response in Leaves of Sugar Beet

Iron nutrient deficiency was investigated in leaves of hydroponically grown sugar beets (Beta vulgaris) to determine how ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) gene expression is affected when thylakoid components of photosynthesis are diminished. Rubisco polypeptide content was reduced by 60% in severely iron-stressed leaves, and the reduction was directly correlated to chlorophyll content. The concentration of Rubisco protein in iron-stressed leaves was found to be regulated by availability of mRNAs, and CO2 fixation by Rubisco was reduced from 45 [mu]mol CO2 m-2 s-1 in extracts from iron-sufficient leaves to 20 [mu]mol CO2 m-2 s-1 in extracts from severely stressed leaves. The rate of CO2 fixation was directly correlated to leaf chlorophyll content. Rubisco in iron-sufficient control leaves was 59% activated, whereas in severely stressed leaves grown under the same light, Rubisco was 43% activated. RNA synthesis was reduced by about 50% in iron-deficient leaves, but 16S and 25S rRNA and ctDNA were essentially unaffected by iron stress.

Stimulated growth and correction of Fe-deficiency with trunk- and foliar-applied methanol-soluble nutrient amendments

Plants treated with nutrient-supplemented methanol showed up to 100% increases in yields when maintained under direct sunlight in desert agriculture. Plants given many applications of aqueous methanol showed symptoms of nutrient deficiency. Supplementation with a source of iron and nitrogen sustained growth, eliminating symptoms of deficiency. Major and minor nutrients were selected for solubility in methanol. Treatment through bark on stems with the formulation corrected nutrient deficiencies in citrus. Foliar application of nutrient supplemented 15% aqueous methanol increased growth and early maturation of rice when applications were made without water stress. Statistical analysis of mature panicle counts and grain yield indicates earlier maturity of methanol treated plants as compared to controls. A photographic technique was utilized to determine Chl status of rice plants.