High relative air humidity and continuous light reduce stomata functionality by affecting the ABA regulation in rose leaves

Plants developed under high (90%) relative air humidity (RH) have previously been shown to have large, malfunctioning stomata, which results in high water loss during desiccation and reduced dark induced closure. Stomatal movement is to a large extent regulated by abscisic acid (ABA). It has therefore been proposed that low ABA levels contribute to the development of malfunctioning stomata. In this study, we investigated the regulation of ABA content in rose leaves, through hormone analysis and β‐glucosidase quantification. Compared with high RH, rose plants developed in moderate RH (60%) and 20 h photoperiod contained higher levels of ABA and β‐glucosidase activity. Also, the amount of ABA increased during darkness simultaneously as the ABA‐glucose ester (GE) levels decreased. In contrast, plants developed under high RH with 20 h photoperiod showed no increase in ABA levels during darkness, and had low β‐glucosidase activity converting ABA‐GE to ABA. Continuous lighting (24 h) resulted in low levels of β‐glucosidase activity irrespective of RH, indicating that a dark period is essential to activate β‐glucosidase. Our results provide new insight into the regulation of ABA under different humidities and photoperiods, and clearly show that β‐glucosidase is a key enzyme regulating the ABA pool in rose plants.     

The effect of fire and permafrost interactions on soil carbon accumulation in an upland black spruce ecosystem of interior Alaska: implications for post‐thaw carbon loss

High‐latitude regions store large amounts of organic carbon (OC) in active‐layer soils and permafrost, accounting for nearly half of the global belowground OC pool. In the boreal region, recent warming has promoted changes in the fire regime, which may exacerbate rates of permafrost thaw and alter soil OC dynamics in both organic and mineral soil. We examined how interactions between fire and permafrost govern rates of soil OC accumulation in organic horizons, mineral soil of the active layer, and near‐surface permafrost in a black spruce ecosystem of interior Alaska. To estimate OC accumulation rates, we used chronosequence, radiocarbon, and modeling approaches. We also developed a simple model to track long‐term changes in soil OC stocks over past fire cycles and to evaluate the response of OC stocks to future changes in the fire regime. Our chronosequence and radiocarbon data indicate that OC turnover varies with soil depth, with fastest turnover occurring in shallow organic horizons (～60 years) and slowest turnover in near‐surface permafrost (>3000 years). Modeling analysis indicates that OC accumulation in organic horizons was strongly governed by carbon losses via combustion and burial of charred remains in deep organic horizons. OC accumulation in mineral soil was influenced by active layer depth, which determined the proportion of mineral OC in a thawed or frozen state and thus, determined loss rates via decomposition. Our model results suggest that future changes in fire regime will result in substantial reductions in OC stocks, largely from the deep organic horizon. Additional OC losses will result from fire‐induced thawing of near‐surface permafrost. From these findings, we conclude that the vulnerability of deep OC stocks to future warming is closely linked to the sensitivity of permafrost to wildfire disturbance.     

Inhibition of RNA Synthesis and the Relationship between Nucleolar and Mitotic Cycles in Zea mays Root Meristems

The relationship between nucleolar and mitotic cycles has beendetermined after treatment of root apices of Zea mays with ethidiumbromide. In the meristematic regions of the stele the two cyclesare not much displaced in relation to each other except fora delay in the onset of the disorganization phase. A few nucleolipersist into metaphase and a few nuclei undergo an amitoticdivision. In the cap initials the drug greatly delays the onsetof disorganization of the nucleolus, which normally occurs beforeprophase in this region. It also delays the completion of reorganizationso that fully organized nucleoli are no longer available duringthe last half of telophase. In the quiescent centre the onsetof disorganization and the end of reorganization of the nucleoliare also delayed in relation to mitosis. There is no evidencefor a delay in the onset of reorganization in any region ofthe meristem. Some cells form multiple micronucleoli and this aberrant behaviouroccurs more often in the cap initials than elsewhere as doesamitotic division.     

SENSORY AND INSTRUMENTAL EVALUATIONS OF TEXTURE IN CHEESES MADE FROM OVINE MILKS WITH DIFFERING FAT CONTENTS

The present study considers the influence of reducing the fat content of ovine milk on the sensory and instrumental texture characteristics of the resulting cheeses. Three manufacturing runs were performed. In each run three cheese batches were manufactured using milks with differing percentage fat contents (8%, 4%, and 2% fat). Analysis of cheese samples was performed at 60, 90, and 120 days of ripening.
The instrumental method used to evaluate cheese texture was uniaxial compression at constant speed, taking readings of stress, strain, and modulus of elasticity (E). Statisticalanalysis revealed differences forboth the differentfat contents and the ripening times considered. Instrumental parameter values increased with lower cheese fat contents; with a 20% reduction in the fat to dry matter content from full-fat to reduced-fat cheeses, resulting in a 35% increase in maximum stress and in the slope of the stress-strain curve at the end of ripening. The greatest sensory differences between samples were recorded for firmness.