Francesca Grisafi

Short-term effects of potassium fertilization on the hydraulic conductance of Laurus nobilis L.

This study reports experimental evidence on the effect of short-term potassium fertilization on potassium uptake, tissue concentration and hydraulic conductance of pot-grown laurel plants. Potassium uptake and loading into the xylem of laurel seedlings increased within 24 h after fertilization. Potassium was not accumulated in roots and leaves, but the [K(+)] of xylem sap was 80% higher in fertilized plants (+K) than in potassium-starved plants (-K), as a likely result of recirculation between xylem and phloem. Increased xylem sap [K(+)] resulted in a 45% increase in transpiration rate, a 30% increase in plant hydraulic conductance (K(plant)) and a 120% increase in leaf-specific conductivity of the shoot (k(shoot)). We suggest that this increase was due to ion-mediated up-regulation of xylem hydraulics, possibly caused by the interaction of potassium ions with the pectic matrix of intervessel pits. The enhancement of hydraulic conductance following short-term potassium fertilization is a phenomenon that can be of advantage to plants for maintaining cell turgor, stomatal aperture and gas exchange rates under moderate drought stress. Our data provide additional support for the important role of potassium nutrition in agriculture and forestry.

Antociani presenti negli ipocotili e nei cotiledoni di plantule di Raphanus sativus L

Abstract Anthocyanin pigments in hypocotyls and cotyledons of Raphanus sativus L. seedlings. - Raphanus sativus L. seedlings growing in darkness do not form anthocyanins. Etiolated seedlings grown in CAP 10−4M, exposed 48 h after sowing to far red light accumulate large quantity of anthocyanins in hypocotyls and cotyledons. This amount of pigments is bigger than that formed by seedlings grown in water and irradiated with white light. However, in both cases, the only anthocyanidin present was pelargonidin and pelargonin the only detectable anthocyanin.

Tamarix arborea var. arborea and Tamarix parviflora: Two species valued for their adaptability to stress conditions.

The choice of stress resistant and highly adaptable species is a fundamental step for landscaping and ornamental purposes in arid and coastal environments such as those in the Mediterranean basin. The genus Tamarix L. includes about 90 species with a high endurance of adversity. We investigated the water relations and photosynthetic response of Tamarix arborea (Sieb. ex Ehrenb.) Bge. var. arborea and T. parviflora DC. growing in an urban environment. Both species showed no evidence of drought or salt stress in summer, and appeared to follow two strategies with T. arborea var. arborea investing in high carbon gain at the beginning of the summer, and then reducing photosynthetic activity at the end of the season, and T. parviflora showing lower but constant levels of photosynthetic activity throughout the vegetative season. For landscaping and ornamental purposes, we suggest T. arborea var. arborea when a fast-growing, high-cover species is necessary, and T. parviflora when less-invasive species are required.

Starch content of etiolated radish (Raphanus sativus L.) hypocotyls as affected by chloramphenicol and external sucrose

Abstract Starch was enzymatically assayed in the hypocotyls of radish (Raphanus sativus L.) seedlings grown in water or chloramphenicol (CAP) 1 × 104. CAP inhibits starch formation and its effect is related to the concentration. Both CAP- and water-grown hypocotyls are able to accumulate starch when sucrose is supplied in the medium, thus suggesting that the damage caused by CAP to the amyloplast is not irreversible. Apical segments of both water- and CAP- grown hypocotyls accumulate starch upon incubation in sucrose solutions while basal segments are unable to accumulate starch even in the presence of sucrose. The authors suggest that the basal segments are unable to perform sucrose uptake or that the amyloplast is incapable to starch synthesis. In any case the inability of the basal segment to perform sucrose uptake is independent of CAP. These findings confirm that the radish hypocotyls is not homogeneous along its axes.

Chloramphenicol effects on adventitious root production by radish hypocotyls

Abstract The excision of the root accelerates greatly the formation of adventitious roots in the hypocotyl of etiolated radish seedlings, but if the seedlings develop in CAP 1×10−4M, no adventitious root are induced after cutting. IAA either alone or associated with CAP, significantly increases the number of primordia in normal hypocotyls if given at the moment of cutting, while it has not stimulatory effect on the hypocotyls of seedlings grown in CAP. IAA has significant effect on both elongation and tickening of hypocotyl segments prepared from seedlings grown in CAP, and this could indicate a specific action of the inhibitor either on a particular process or on particular cells. The endodermis and the pericycle, which are the two cell layers implicated in the formation of the adventitious roots, could be the mediators of this particular effect of CAP in rooting.