Morpho-physiological plasticity contributes to tolerance of Calluna vulgaris in an active geothermal field

Geothermal alteration fields are very prohibitive environments, limiting vegetation establishment and growth. In the present study, the ecological specialisation of the pioneer plant Calluna vulgaris (L.) Hull was investigated, assuming that its ability to survive in geothermal habitats derives from a fine regulation of morpho-physiological traits. Mature leaves of C. vulgaris were sampled from plants close to a fumarole (near), and from plants living at a distance of some metres (intermediate) or ~1 km (distant) from a fumarole. Along the sampling sites, a gradient of soil-pH and temperature values occurred, with near plants facing the highest soil temperature and the lowest soil pH. A regulation of constitutive morpho-anatomical and physiological traits in response to different stress levels occurred. A progressive reduction of leaf exposed surface and hair density and mucilages, combined with a gradual increase of oxidative stress levels, of phenols and ascorbate, was observed from distant to near plants. Near plants showed an increase in stomatal density and in lignin and cuticle thickness, and the highest activity of ascorbate peroxidase. Except for high glutathione concentrations, in distant plants antioxidant machinery was consistently less active. The apparent morphological and physiological plasticity demonstrated in the present research contributed to the capability of these plants to tolerate the prohibitive, highly changing environmental conditions of the geothermal field

LA RISPOSTA ADATTATIVA AGLI STRESS ECOLOGICI DEGLI AMBIENTI DUNALI: TRE EUPHORBIACEAE A CONFRONTO

Le dune costiere rappresentano un ambiente estremo, dominato da condizioni di aridità e grande mobilità del substrato, dall’aerosol marino, dalla forte irradianza solare e dalle elevate temperature. La vegetazione caratteristica dei litorali sabbiosi è per questo rappresentata da un numero limitato di specie. In questo studio sono stati analizzati gli adattamenti morfo-funzionali della foglia di tre Euphorbiaceae presenti sui litorali sabbiosi della Toscana: Chamaesyce peplis (L.) Prokh. (ex Euphorbia peplis), pianta annuale presente sulla spiaggia emersa; Euphorbia paralias L., specie perenne tipica delle dune embrionali ed Euphorbia terracina L., pianta con ciclo biologico da annuale a perenne presente sia sulle dune embrionali che sulle dune mobili. Le foglie delle tre Euphorbiaceae studiate presentano un diverso orientamento nello spazio: in C. peplis l’orientamento è plagiotropo ma la lamina revoluta, riduce la superficie esposta alla radiazione solare; E. paralias ed E. terracina hanno foglie ortotrope ed appressate al fusto, adattamento che protegge la pagina superiore della foglia dall’irraggiamento solare. Tutti e tre i taxa presentano cellule epidermiche con parete e cuticola ispessite per evitare la perdita di vapore acqueo. In particolare, l’epidermide di C. peplis ed E. paralias è formata da cellule papillose in grado di riflettere parte della luce incidente sulla foglia. Una caratteristica peculiare di C. peplis è la presenza di cristalli di sale lungo le pareti radiali e la parete tangenziale interna delle cellule epidermiche probabilmente coinvolte anche nell’accumulo e/o nell’eliminazione dei sali. Per quanto riguarda la distribuzione degli stomi, C. peplis ed E. terracina presentano numerosi stomi su entrambe le facce, con cellule di guardia ricche di amido; mentre in E. paralias gli stomi sono presenti solo sulla superficie adassiale. E. terracina, inoltre, ha stomi di dimensioni ridotte rispetto a quelli delle altre due specie, ma presenta una maggiore densità. C. peplis ed E. terracina hanno uno spesso mesofillo costituito da parenchima a palizzata su entrambe le facce e nella parte centrale, da parenchima acquifero (particolarmente sviluppato in Chamaesyce, la più esposta alla salinità dell’ambiente dunale). In Euphorbia paralias il mesofillo è formato da un aerenchima con ampi spazi intercellulari che possono rappresentare un’importante riserva di CO2 per la foglia. Per quanto riguarda i tratti funzionali, E. paralias si differenzia per i valori di SLA (area fogliare specifica) più bassi rispetto a C. peplis ed E. terracina che non presentano differenze significative tra loro; e di LDMC (contenuto fogliare di sostanza secca) comparabili a quelli trovati in E. terracina ma significativamente più alti rispetto a C. peplis. Questi dati indicano come E. paralias mostri una maggiore resistenza allo stress ambientale, necessaria in una pianta perenne. I valori relativi ad SI (indice di succulenza), invece, sono significativamente più alti in C. peplis, intermedi in E. paralias e più bassi in E. terracina. Quest’ultimo risultato riflette la distribuzione spaziale delle tre specie lungo il gradiente di salinità spiaggia-duna. In conclusione, queste evidenze sperimentali testimoniano come la risposta adattativa delle specie vegetali agli stress ricorrenti tipici dell’ambiente dunale possa essere plastica e differente, anche in specie appartenenti alla stessa famiglia

Dynamics of Pollen Grain Germination in Two Cultivars of Malus domestica: the Influence of Actinomycin D on Fresh and Stored Pollen Grains

The pattern of germination has been detected in the presence or in the absence of Actinomycin D (AmD) in fresh and stored binucleate pollen grains of' Golden Delicious' (GD) and' Starkrimson' (S). Pollen tube growth consisted of two distinct phases, autotrophic and heterotrophic, in both fresh and stored pollen grains. The pollens of the two cultivars differ: (i) in the length of the first phase, being 3 h in GD and 2 h in S, and (ii) in the response to storage. As far as the response to storage is concerned the cultivar S seems to be more damaged than GD when the storage effect is evaluated as the first phase length; less damaged than GD when the effect is expressed as tube length

RNA-SYNTHESIS IN THE EMBRYO SUSPENSOR OF PHASEOLUS-COCCINEUS AT 2 STAGES OF EMBRYOGENESIS, AND THE EFFECT OF SUPPLIED GIBBERELLIC-ACID

RNA synthesis in giant cells containing polytene chromosomes in the embryo suspensor of Phaseolus coccineus was analyzed by autoradiography after [ 3H]-uridine treatment. Embryos at the heart-shaped stage of development and at a cotyledonary stage were studied. Discontinuous labelling of the polytene chromosomes was always observed. The chromosomes were subdivided into segments (chromosome regions) which behaved as functional units, since discontinuous labelling was never seen within any of the regions. It was found that most chromosome regions were engaged in RNA synthesis to different degrees at the two embryo developmental stages. Regions showing identical labelling patterns tended to lie close together in the chromosome arms and to keep their functional activity coordinated at both stages of embryo development. The chromosome regions bearing 18 S+25 S ribosomal genes were never simultaneously active in RNA synthesis and different regions were preferentially transcribed at each stage of embryo development. However, at both stages, all the chromosome regions bearing 5 S ribosomal genes showed comparable labelling frequencies. The effect on transcription of gibberellic acid (GA 3) treatments was also studied. At both embryo developmental stages, GA 3 enhanced the rate of RNA synthesis in the polytene suspensor cells. The frequency with which certain chromosome regions were transcribed was also increased significantly (P≤0.001) and this stimulatory effect was greater in embryos at the cotyledonary stage than in heart-shaped embryos. At the latter developmental stage, RNA synthesis was repressed by GA 3 in a few chromosome regions. These results are discussed briefly in relation to previous findings using different methods of studying the organization of polytene chromosomes and the functional activity of the embryo suspensor of Phaseolus coccineus