Somatic hybridization in mint: identification and characterization of Mentha piperita (+) M. spicata hybrid plants

 Twenty eight somatic hybrid plants were identified following protoplast fusions between peppermint (Mentha piperita L. cv Black Mitcham), producing high-quality oil, and spearmint (Mentha spicata L. cv Native Spearmint), likewise producing high-quality oil and also possessing resistance to verticillium wilt. Prior to fusion, peppermint protoplasts were subjected to iodoacetic acid to inhibit cell division. Protoplasts of peppermint and spearmint were fused using polyethylene glycol plus DMSO. Fusion products were cultured according to an efficient protoplast-to-plant-cycle protocol developed for peppermint. Using this protocol, iodoacetic acid-treated peppermint protoplasts were not able to divide, whereas untreated spearmint protoplasts had the ability to produce callus but not shoots. Therefore, selection of somatic hybrid calli was based on the presumed capability of hybrid cells to form calli and shoots. Shoots in vitro were initially identified as hybrids using RAPD profiles. Subsequently, observations on morphology, chromosome counts, and Southern-hybridization patterns confirmed their hybrid status. The results of verticillium tests revealed that 18 somatic hybrids were more susceptible than Native Spearmint, while hybrid II-14 had a level of susceptibility intermediate between that of the fusion parents. Oil-analysis of hybrid plants indicated that they all have a GC-profile typical of spearmint oil. Received: 8 February 1997 / Accepted: 9 April 1997     

Variation in Growth Rates under Saline Conditions of Pascopyrum smithii (Western Wheatgrass) and Distichlis spicata (Inland Saltgrass) from Different Source Populations in Kansas and Nebraska: Implications for the Restoration of Salt-Affected Plant Communities

Soil salinization resulting from agricultural and oil‐ and gas‐production activities can impact habitats of native flora and fauna and reduce production on agricultural lands. Restoration of saline areas with salt‐tolerant vegetation may alleviate impacts. However, differences in how the growth rate under saline conditions varies between species and source populations must first be evaluated before recommending species for restoration. Plant material of Western wheatgrass (Pascopyrum smithii) and Inland saltgrass (Distichlis spicata) collected from Cheyenne Bottoms Preserve, Kansas and Little Salt Fork Marsh, Nebraska was propagated to evaluate variation in growth rates between these species under saline conditions and determine if differences exist between populations within these species. Ten transplants of each species from each location were grown in sand culture in a greenhouse for 51 days and watered with one of five different saltwater solutions (0.86 dS/m, 9.85 dS/m, 17.85 dS/m, 32.5 dS/m, and 57.7 dS/m). Results indicate that P. smithii grew faster than D. spicata at all comparable salinity levels. Only D. spicata exhibited significant differences in growth rate under saline conditions between populations. Results suggest that P. smithii is equivalent to D. spicata in salt tolerance and should be regarded as an appropriate halophyte for restoration of salt‐affected plant environments. Results for D. spicata suggest that differences between source populations should be considered when evaluating plant material for plant community restoration.     

Diurnal variation in the temperature response of leaf extension of two bunchgrass species in the field

The effect of temperature on short-term leaf extension rates was studied for two cool-season tussok grasses, Agropyron desertorum and Pseudoroegneria spicata, growing in the field under a variety of water stress and defoliation conditions. Leaf extension rates and air temperatures were monitored every half hour during numerous 12- to 65-h periods in three growing seasons using auxanometers constructed of precision resistors. For both species, a three-phase relationship between leaf extension rate and temperature was observed during diurnal cycles. Leaf extension rate increased linearly with temperature from dawn until midday (phase 1). Leaf extension then increased rapidly, reaching maximum rates in the early evening (approximately 1900h), despite decreasing temperatures during this period (phase 2). Finally, leaf extension rate declined with temperature from evening until dawn (phase 3). This diurnal cycle was described by linear (phase 1) and quadratic (phases 2 and 3 combined) regression models. Although the rate of leaf extension and daily integrals were affected by the water stress and defoliation treatments, the diurnal pattern was consistently observed. Temperature was probably a major factor governing leaf extension rates at night (phase 3), but it appeared unimportant in controlling leaf extension between dawn and midday. The relative importance of physiological and environmental factors controlling leaf extension rate appears to shift during the day in these species under field conditions.     

The influence of herbivory on plant cover and species composition in the Pryor Mountain Wild Horse Range,USA

We investigated the effects of short- and long-term ungulate grazing on plant species cover and composition in arid lowland and more mesic upland communities of the Pryor Mountain Wild Horse Range (PMWHR). Measurements were taken over two years which differed significantly in growing season precipitation. Interannual differences in plant cover were significantly greater than differences between grazed and ungrazed communities. In the arid lowlands total plant cover decreased from 47% in 1993, a relatively wet year, to 29% in 1994, a relatively dry year. In the more mesic uplands total plant cover decreased from 107% in 1993 to 56% in 1994. The magnitude of change in cover was greatest in the grasses, especially for Pseudoroegneria spicata, the most abundant species in the lowland communities, which decreased from 21% cover in 1993 to 11% in 1994. There was not a consistent effect of herbivory on plant cover across sites, but its effects, particularly on the dominant perennial grasses, were conspicuous at some sites. For instance, in the lowlands cover of P. spicata was 3–12% in long-term grazed sites and 9–28% in short- to long-term ungrazed sites. Our study indicates that abiotic factors (e.g., precipitation) are more likely than grazing to affect abundances of key plant species, and hence ecosystem dynamics, in the PMWHR, and that the effects of herbivory are more localized and more prevalent in the lowland grasses than in the other plant functional groups.     

Deterring rodent seed‐predation using seed‐coating technologies

With many degraded environments undergoing restoration efforts, there is a growing need for the optimization of direct seeding practices. Seeds planted on wildlands are often consumed by rodents, leading to reduced plant establishment. Coating seeds in rodent aversive products may prevent seed‐predation. We tested 10 seed‐coating formulations containing products expected to deter rodents, namely: ghost and cayenne pepper powders; essential oils from bergamot, neem, and pine; methyl‐nonyl‐ketone, anthraquinone, activated carbon, beta‐cyclodextrin, and a blank coating containing no rodent deterrents to serve as a control treatment. Each treatment was applied to Pseudoroegneria spicata (bluebunch wheatgrass) seeds. These seeds germinated similarly to uncoated control seeds unless the coating contained methyl‐nonyl‐ketone which reduced germination. When seeds were offered to Ord's kangaroo rats (Dipodomys ordii), they strongly avoided the treatments in favor of uncoated control seeds. Notably, the blank coating, lacking active ingredients, still elicited 99% avoidance. However, these results indicated behavior when alternative food sources are readily available, a scenario rare in nature. To address this, a second feeding experiment was conducted to observe D. ordii's behavior under calorie‐restricted conditions. D. ordii were subjected to a fast period, then offered only one treatment. Under these conditions, many subjects chose to consume coated seeds, but to a lesser degree than subjects offered control seeds. Seeds coated in ghost pepper, neem oil, and activated carbon reduced consumption by 47–50%. Given these lab results, we would expect these treatments to increase native plant establishment following the direct seeding of wildlands by protecting seeds from rodent predation.     

Proteomic snapshot of spearmint (Mentha spicata L.) leaf trichomes: A genuine terpenoid factory

Peltate glandular trichomes from Mentha spicata were purified on a Percoll gradient and soluble and membrane proteins were trypsinized and the peptides were separated by nano‐LC fractionation and analyzed by MALDI‐MS/MS. The vast majority of the 1666 proteins identified were housekeeping proteins or involved in the primary metabolism. However, 57 were predicted to be involved in the secondary metabolism. Of these, 21 were involved in the synthesis of phenylpropanoids and phenolics and 32 in terpenoid synthesis. Of the 14 membrane transporters identified, the 11 ATP‐binding cassette transporters provide good material for assessing whether active transport is required for the transfer of monoterpenoid intermediates between cellular compartments and for the secretion of the final products into the subcuticular storage cavity. In conclusion, this proteome analysis of M. spicata peltate trichomes has identified several candidate proteins that might be involved in terpenoid synthesis and transport. The data have been deposited to the ProteomeXchange with identifier PXD000352 ( http://proteomecentral.proteomexchange.org/dataset/PXD000352 ).     

Exploiting wild population diversity and somaclonal variation in the salt marsh grass Distichlis spicata (Poaceae) for marsh creation and restoration

The salt marsh grass Distichlis spicata was regenerated from tissue culture and propagated in a greenhouse. Selected regenerants, along with selections from six wild populations, were grown for two years in a common garden flood-irrigated thrice weekly with tidal creek water. Selected wild and regenerated plants were also planted in a created salt marsh. Significant differences among regenerant and wild population selections were found in several functionally important salt marsh plant characteristics, including potential detritus production, belowground organic matter production, canopy structure, and decomposition rate. A combination of characteristics not found in the wild populations was evident in a regenerated line that exhibited both a high detritus production potential and a high decomposition rate. The amount of variation that occurred among regenerants from one parental line via somaclonal variation was similar to that which occurred among the wild population selections. Results of this study suggest that tissue culture may provide a means of producing marsh grasses with specific characteristics for directing the functional development of newly created salt marshes.     

Effects of salinity on chlorophyll fluorescence and CO<Subscript>2</Subscript> fixation in C<Subscript>4</Subscript> estuarine grasses

The effects of salinity (sea water at 0 ‰ versus 30 ‰) on gross rates of O₂ evolution (J _O2) and net rates of CO₂ uptake (P _N) were measured in the halotolerant estuarine C₄ grasses Spartina patens, S. alterniflora, S. densiflora, and Distichlis spicata in controlled growth environments. Under high irradiance, salinity had no significant effect on the intercellular to ambient CO₂ concentration ratio (C _i/C _a). However, during photosynthesis under limiting irradiance, the maximum quantum efficiency of CO₂ fixation decreased under salinity across species, suggesting there is increased leakage of the CO₂ delivered to the bundle sheath cells by the C₄ pump. Growth under salinity did not affect the maximum intrinsic efficiency of photosystem 2, PS2 (F_V/F_M) in these species, suggesting salinity had no effect on photosynthesis by inactivation of PS2 reaction centers. Under saline conditions and high irradiance, P _N was reduced by 75 % in Spartina patens and S. alterniflora, whereas salinity had no effect on P _N in S. densiflora or D. spicata. This inhibition of P _N in S. patens and S. alterniflora was not due to an effect on stomatal conductance since the ratio of C _i/C _a did not decrease under saline conditions. In growth with and without salt, P _N was saturated at ∼500 μmol(quantum) m⁻² s⁻¹ while J _O2 continued to increase up to full sunlight, indicating that carbon assimilation was not tightly coupled to photochemistry in these halophytic species. This increase in alternative electron flow under high irradiance might be an inherent function in these halophytes for dissipating excess energy.