Interactions between hosts and non-hosts of Pinus spp. and Matsucoccus josephi: anatomical responses of stem to infestation

Artificial infestation of seven pine species revealed that Matsucoccus josephi (Homoptera: Margarodidae) completes its development on Pinus brutia , P. eldarica and P. halepersis , whereas only a small number of the scale larvae infesting P. cunariensis and P. pined reached the second instar and none developed to the adult stage. M. josephi crawlers died while trying to feed on P. radiata and P. pinaster. Histological examination of the infested plant sections indicated that necrosis in shoot and stem barks of P. eldarica and P. halepensis occurs just before or after the scale completes its development. Injury reached the cambium, and traumatic resin ducts; parenchyma cells instead of tracheids and curved tracheids were formed. In P. brutia wound periderm was observed in the stem section but not in the shoot cortex following scale development. Wound periderm was also formed in the stem cortex of P. canariensis and P. pinena whereas no pathological changes were detected in the infested cortex of P. pinaster and P. radiata.
Mechanical lesions caused by needle punctures resulted in the production of parenchyma cells instead of tracheids in all four pine species investigated. The response of the pine cortex was non-specific; however several similarities in the response to scale infestation, such as the formation of resin ducts, were observed. We hypothesize that the response of the pine tissue to the scale saliva is a hypersensitive reaction. It is suggested that the development of Matsucoccus species on particular pine species is related to the scale's inability to trigger the defence system of the host while the larvae are feeding.     

Osmotic Adaptation in Panicum repens. Differences Between Organ, Cellular and Subcellular Levels

The process of osmotic adaptation was studied in leaves of Panicum repens. Two phases were observed: the first phase, which continued for 2–4 days, was mainly characterized by dehydration of leaves, a fast synthesis of organic acids and penetration of sodium into leaf cells. Chloride becomes dominant in the leaves only from the third day of exposure and onwards. The second phase of adaptation lasted for 4–6 days. During this phase, a decrease in organic acid content and an increase in leaf-chloride content was observed. In spite of the fact that the osmotic potential of the leaves reached lower values than that of the external medium already after 2 days, the rate of growth of the plants was hampered. Such inhibition of growth disappeared 6–8 days after exposure to salinity. Ion content of the cell walls, chloroplasts and vacuoles of Panicum leaf cells was investigated during the various stages of osmotic adaptation. An increase in sodium and chloride content of the cell walls during the early period of adaptation probably prevented the full osmotic adaptation of the protoplasts. It is suggested that a locally unbalanced distribution of ions may be one of the reasons for the decrease in growth rate during the process of osmotic adaptation and frequently after that.     

Unseasonable Latewood and Incrusted Pits are the Cause of Drying in Pinus halepensis and P. eldaricaInfested with Matsucoccus josephi

Mendel, Z. and Liphschitz, N. 1988. Unseasonable latewood andincrusted pits are the cause of drying in Pinus halepensis andP.eldarica infested with Matsucoccus josephi.—J. exp. Bot.39: 951–959. A study was made of the effects of Matsucoccus josephi (Insecta:Homoptcra: Margarodidae) on (a) water transport in Pinus halepensis,using a basic fuchsin solution and (b) the structural changesof the xylem of Pinus halepensis, P. brutia andP. eldarica usinga scanning electron microscope.Examinations were carried outin artificially and naturally infested plants. Transport ofthe fuchsin dye was arrested below the affected zone of heavilyinfested shoots, but reached the shoot apex through sparselyinfested segments or via segments heavily infested with thefirst larval stage. Heavily infested stem sections of P. halepensisand P.eldarica were characterized by narrow pits and incrustedpit membranes. In non-infested shoots and those infested withfirst or early second-scale larvae in both these species andheavily infested P. brutia shoots, there were typical earlywoodpits with wide pit apertures and thin membranes. It is suggestedthat blocking of water ascent in P. halepensis and P. eldaricastarts when female second-instar larvae complete their developmentand only when population density is relatively high. Therefore,it is considered that the accelerated drying of the growth ofP. halepensis and P. brutia is directly related to the narrowingof the pit apertures, which resembled those of latewood pitsalthough produced early in the season. The absence of changesin the xylem of heavily infested P brutia may explain why thisspecies tolerates a high density of M. josephi. The structuralmodification of the xylem caused by the scale may be relatedto imbalance in plant growth hormones which are either transmittedwith the insect saliva or formed in the plant by salivary enzymes. Key words: Xylem, Matsucoccus, Pinus     

Salt Glands on Leaves of Rhodes Grass (Chloris gayana Kth.)

Existence of salt glands on leaves of Chloris gayana is established.Such glands are comprised of two cells: a basal large cell andan upper small one. The secreted salts crystallize in a formof whiskers on top of the upper gland cell. The significanceof the process is discussed.     

Cambial Activity in Zygophyllum dumosum Boiss

Cambial activity in Zygophyllum dumosum Boiss.—a dominantdesert shrub in Israel—was investigated. Cambial activityin young plants seems to be greatly affected by water supply,while cambial activity in old specimens was found to be moreendogenously controlled. A late-summer cambial dormancy wasobserved under field conditions even in plants that were irrigated.     

The Annual Rhythm of Activity of the Lateral Meristems (Cambium and Phellogen) in Cupressus sempervirens L

The annual rhythm of cambial activity in Cupressus sempervirensseems to be endogenous and fits well the Mediterranean climaticrhythm. Under outdoor conditions the cambium begins its activitytowards the autumn when temperatures drop and water is lesslimiting. The cambium continues to be active during the mildMediterranean winter and enters dormancy towards the beginningof the dry summer. A constant supply of water is not enoughto avoid cambial dormancy but may result in earlier onset anda prolonged period of activity. Relationships between xylemand phloem production, between shoot and root, and between cambialand phellogen activity are discussed. Cupressus sempervirens L., cypress, cambium, phellogen, annual rhythm, wood production