Responses of the bed bug,Cimex lectularius,to temperature extremes and dehydration: levels of tolerance,rapid cold hardening and expression of heat shock proteins

This study of the bed bug, Cimex lectularius, examines tolerance of adult females to extremes in temperature and loss of body water. Although the supercooling point (SCP) of the bed bugs was approximately −20°C, all were killed by a direct 1 h exposure to −16°C. Thus, this species cannot tolerate freezing and is killed at temperatures well above its SCP. Neither cold acclimation at 4°C for 2 weeks nor dehydration (15% loss of water content) enhanced cold tolerance. However, bed bugs have the capacity for rapid cold hardening, i.e. a 1‐h exposure to 0°C improved their subsequent tolerance of −14 and −16°C. In response to heat stress, fewer than 20% of the bugs survived a 1‐h exposure to 46°C, and nearly all were killed at 48°C. Dehydration, heat acclimation at 30°C for 2 weeks and rapid heat hardening at 37°C for 1 h all failed to improve heat tolerance. Expression of the mRNAs encoding two heat shock proteins (Hsps), Hsp70 and Hsp90, was elevated in response to heat stress, cold stress and during dehydration and rehydration. The response of Hsp90 was more pronounced than that of Hsp70 during dehydration and rehydration. Our results define the tolerance limits for bed bugs to these commonly encountered stresses of temperature and low humidity and indicate a role for Hsps in responding to these stresses.     

Inheritance and fitness effects analysis for a euchromatic supernumerary chromosome segment in Scilla autumnalis (Liliaceae)

A large euchromatic supernumerary segment (ss) occurs at a high frequency in a natural population of Scilla autumnalis from the west of the Iberian Peninsula. Mother-offspring analyses have shown random pollination of all bulbs lacking the extra segment but non-random pollination of some bulbs carrying it. With a single exception, ss transmission appeared to be Mendelian through the eggs of heterozygous bulbs, which was consistent with results of controlled crosses. An analysis of the effects of this ss on some female fitness components demonstrated significant differences between genotypes for mean seed weight. Heterozygous bulbs yielded significantly heavier seeds than standard homozygous bulbs, and slightly (but not significantly) heavier seeds than segment homozygotes. No trade-off was observed between seed number and seed size in this population. In heterozygotes there was a surprising positive correlation between fruit fertility (number of seeds per fruit) and seed weight. These results are discussed in relation to the maintenance of the segment in natural populations.     

Studies on Foliar Penetration: V. FACTORS CONTROLLING THE PENETRATION OF 2,2-DICHLOROPROPIONIC ACID (DALAPON) INTO THE LEAVES OF PHASEOLUS VILGARIS

The factors which control the penetation of 2,2-dichloropropionicacid (dalapon), containing ³⁸Cl, into leaf disks of Phaseolusvulgris have been investigated. In many respects the patternof penctration resembles that already reported for 2,4-dichlorophenoxyaceticacid (2,4-D) but in others the results dispaprate. In darknessthe rate of penetration is proportional to the external concentration,remains constant over at least 24 h, is unaffected by 3-(3,4-dichlorophenyl)-1,1-dimethlyrea(DCMU), and has a temperature coefficient ranging from 1.6 to2.3. Light intensities as low as 1500 lx enhance penetrationat both surfaces but, whereas the responses at the abaxial surfacea maximum at 10.000 lx, at the adaxial surface penetration continuesto increase slightly as the intensity is raised to 21 500 lx.After 4 or 8 h at the higher light intersities an accelertedphase of penetration is initiated, which is sensitive to bothlow temperature and DCMU. When leaf disks, exposed to dalaponin darkness,are translated to buffer, there is no outward diussusion,nor on adding non-radioactive dalapon does exchange take place.Dalapon taken up in the light is less firmly bound: it failsto diffuse out, but partial exchange is found. While penetrationfalls as the external pH is raised to 5.2, significant amountscontinue to enter which are unaffected by p H as the latteris raised to values which cause almost complete dissociation.It is concluded that, as with 2,4-D, uptake in light is ATP-drivenand both polar and non-polar pathways appear to be involvedduring penetration.     

The Effect of the Fruit and Exogenous Hormones on Leaf Expansion and Composition in Citrus

Sanz, A., Martinez Cortina, C. and Guardiola, J. L. 1987. Theeffect of the fruit and exogenous hormones on leaf expansionand composition in Citrus.—J. exp. Bot. 38: 2033-2042. The effect of the developing flowers and fruitlets on leaf expansionand composition has been determined in leafy inflorescencesof Citrus sinensis L. Osbeck. During leaf expansion the developingflowers do not compete with the leaves, and their early removaldoes not affect leaf size and composition. Competition for mineralelements is established after flower opening, once leaf expansionis complete. No effect of the fruit on metabolizable carbohydratesin the leaves was found up to day 22 after flower opening. The response to exogenously applied growth regulators suggeststhat the differences in weight and composition between inflorescenceleaves and leaves from vegetative sprouts may be due to hormonally-mediateddifferences in sink strength. Gibberellic acid enhances laminaexpansion and increases the sink strength of the leaves. Kinetinenhances lamina expansion without affecting sink strength. Leafgrowth is directly related to both soluble and wall-bound acidinvertase activities; however, the GA₃ effects on leaf growthand sink strength are unrelated to invertase activity and tothe rate of starch accumulation. Key words: Acid invertase, amylase, carbohydrates, Citrus, leaf growth     

Morphological and architectural features of young Nothofagus pumilio (Poepp. & Endl.) Krasser (Fagaceae)

The morphology and architecture of young Nothofagus pumilio plants growing as understorey and in a cleared area were assessed. Length, number of internodes, presence of branches and apex condition were registered for each growth unit (GU) in the sampled plant. GUs were grouped according to branching order and age of the bearing axis. Understorey plants were seven years old and had a short trunk bearing 2–3 orders of branches; all of their most recent GUs were horizontal and of comparable size. Plants growing in the cleared area were 10–16 years old and had a vigorous vertical and dominant trunk bearing 4–5 orders of less vigorous, horizontal branches. Plants from the cleared area showed signs of having had comparable-size GUs in all of their axes at a younger stage of growth. N. pumilio plants appear to start their growth with the production of short GUs in all of their axes irrespective of the light conditions. In contrast, the development of a vertical, vigorous trunk, seems to be restricted to plants growing in open environments.