ABSTRACIOsmotic adjustment in Rosa hybrida L. cv Samantha was characterized by the pressure-volume approach in drought-acclimated and unacclimated plants brought to the same level of drought strain, as assayed by stomatal closure. Plants were colonized by either of the vesicular-arbuscular mycorrhizal fungi Glomus deserticola Trappe, Bloss and Menge or G. intraradices Schenck and Smith, or were nonmycorrhizal. Both the acclimation and the mycorrhizal treatments decreased the osmotic potential (*,P) of leaves at full turgor and at the turgor loss point, with a corresponding increase in pressure potential at full turgor. Mycorrhizae enabled plants to maintain leaf turgor and conductance at greater tissue water deficits, and lower leaf and soil water potentials, when compared with nonmycorrhizal plants. As indicated by the *i',, at the turgor loss point, the active *I. depression which attended mycorrhizal colonization alone was 0.4 to 0.6 megapascals, and mycorrhizal colonization and acclimation in concert 0.6 to 0.9 megapascals, relative to unacclimated controls without mycorrhizae. Colonization levels and sporulation were higher in plants subjected to acclimation. In unacclimated hosts, leaf water potential, water saturation deficit, and soil water potential at a particular level of drought strain were affected most by G. intraradices. G. deserticola had the greater effect after drought preconditioning.Recent evidence suggests that colonization of root systems by VA2 mycorrhizal fungi affords host plants greater resistance to drought stress3 (2,22). Mycorrhizal plants may avoid drought to some extent through enhanced water uptake at low soil moisture levels (26). In onion the effect appears to be conferred through improved phosphorus nutrition (22) 'The terminology of Levitt (18) has been employed throughout this paper in distinguishing an environmental limitation ('stress') from the related plant response to the limitation ('strain).potential has been observed in wheat (2); however, definitive studies on osmotic adjustment in mycorrhizal plants are lacking. The influence of drought-acclimation and mycorrhizal colonization on tissue water relations and osmotic response in equally sized and adequately P-nourished rose plants is reported in this study. As drought may modify the partitioning of water into apoplastic and symplastic fractions (24), parameters for estimating these fractions were also calculated. MATERIALS AND METHODS

SUMMARYPlants of Rosa hybrida L. cv. ' Samantha', grown with high or low phosphorus (P) fertilization, were inoculated with Glomus intraradices Schenck & Smith, G. deserticola Trappe, Bloss & Menge, or left non-mycorrhizal. All plants except the low-P non-mycorrhizal group had similar tissue dry weights, leaf and root surface areas, growth ratios, stomatal characteristics and P contents. The higher rate of P fertilization increased plant dry weight three-fold and leaf area four-fold in non-mycorrhizal plants, but had no effect on growth characteristics of mycorrhiz^al plants except for a depression of colonization levels. Under well-watered conditions (75-90% and 45-50% relative soil water content, 6), low-P mycorrhizal plants displayed greater leaf conductance (g) than both high-P mycorrhizal and non-mycorrhizal plants. Leaf water potential {r/r) was similar in colonized and uncolonized roses. Fungal species did not differ significantly in their influence on ^ or g.

The role of ethylene and auxins in flood-induced adventitious root formation and hypocotyl hypertrophy in sunflower {Helianthus annuus L. cv. Russian) plants was studied. Flooding without aeration (F) resulted in a steady increase in ethylene in hypocotyls, and flooding with aeration (FA) caused a transient increase. Low light intensity increased ethylene levels but decreased adventitious root formation. Treatment of shoots with benzyladenine (BA) increased ethylene content in non-flooded (NF) but not in F or FA shoots.Twenty-four hours of flooding brought about a rise of endogenous indole-acetic acid (IAA) in hypocotyls. ^''C-IAA applied to the shoot accumulated more in F and FA hypocotyls than in NF hypocotyls, and BA reduced this accumulation. There was less IAA metabolism in F and FA than in NF hypocotyls.Tri-iodo benzoic acid (TIBA) applied to the hypocotyls of F plants inhibited root production. Benzyladenine (BA) applied to the leaves had similar effect but was not effective when supplied to the shoot apex. BA did not inhibit flood-induced hypocotyl hypertrophy. Ethrel did not affect adventitious root formation in NF plants but did increase hypocotyl thickening.It is concluded that flood-induced adventitious root formation is stimulated primarily by an accumulation of auxins in the hypocotyls. Increases in ethylene might cause this auxin build up. Hypocotyl hypertrophy is presently thought to be the result of an interaction of auxin and ethylene with ethylene being the major factor.

No abstract

Natural cork enclosures, due to their cell structure, composition, and low moisture are fairly transparent to terahertz (THz) and millimeter waves enabling nondestructive evaluation of the cork's surface and interior. It is shown that the attenuation coefficient of the defect-free cork can be modeled with a Mie scattering model in the weakly scattering limit. Contrast in the THz images is a result of enhanced scattering of THz radiation by defects or voids as well as variations in the cork cell structure. The presence of voids, defects, and changes in grain structure can be determined with roughly 100-300 microm resolution.