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Two dry bean (Phasaolua vulgarla L.) cultivars, one susceptible (PI-165078 (PI)) and one resistant (Great Northern Valley (GNV)) to Fe deficiency chlorosis in the field were grown in a modified Hoagland solution in a growth chamber under varying degrees of Fe stress (0.0, 0.05, 0.10, and 1.0 mg Fe/liter). Response to Fe-deficiency stress was determined by measuring daily release of H ions and reductant from the roots, leaf chlorophyll and concentrations of Fe and Mn in leaves and roots. As the plants responded to Fe stress, both varieties released H ions and reductant from their roots, with GNV responding sooner than PI. There were generally no significant differences between cultivars in chlorophyll concentration. The Fe concentration in top leaves was not significantly different between cultivars at solution Fe levels below 1 mg/liter. There was some indication that GNV might be more Fe-efficient at the 0.05 mg Fe/liter treatment than PI, but these two dry bean cultivars are similar enough in their response to Fe-deficiency stress for both to be designated Fe-efficient.

To contribute to further understanding of damage mechanisms in silicon induced by picosecond Nd:YAG 1.06-μm laser pulses, the damage at laser intensities below the one-shot damage threshold has been studied. By using a biased charge-collection wire or electron-multiplier tube, one can detect the charge emitted during small pit formation, which may be considered as the initial damage morphology. The investigation of the incubation period has been conducted by observing the first charge emission, which indicates its termination. This incubation time is analogous to the lifetime of the solids subject to a repeated mechanical load and is characterized by processes that are irreversible for at least 3 sec. This suggests that the damage precursors are long-lived excitations or an accumulation of permanent states. The heterogeneous nature of the nucleation of damage suggests that these precursor states act as nucleation seeds to the laser-induced damage. Charge emission after the incubation period was also studied. Positive and negative particles are emitted equally after damage initiation, probably because of thermal evaporation of silicon from small regions. The charge emission follows the Arrhenius relation. Experimentally, this result was independent of pulse-repetition period up to at least 10 sec. Damage morphology was compared to charge emission and suggests that charges are emitted mainly from pits, grooves, and holes within the damaged area.

Soil drenches containing 250 μg of paclobutrazol or uniconazol (50 ml of a 17 μM solution) reduced the height of both corn (Zea mays L. cv. How.Sweet It Is) and soybean (Glycinemax (L.) Merr. cv. A2) seedlings. With corn, uniconazol was considerably more active than paclobutrazol in reducing height whereas with soybean both compounds had similar dwarfing effects. The compounds increased foliar chlorophyll content and leaf thickness in soybean but had no effect on these parameters in corn. The increase in leaf thickness with soybean was due primarily to an increase in the thickness of the palisade cell layer. Chloroplast size and ultrastructure of both species were unaffected by the compounds. The growth regulators increased root diameter in both corn and soybean because of increased size of cortical parenchyma cells and particularly in soybean because of radial rather than longitudinal growth of the first few layers of the cortical parenchyma.

Iron efficiency in A7 soybean [Glycine max (L.) Merr.] was increased through plant breeding, and it was determined in a companion paper that A7 soybean responded to Fe-deficiency stress by increased exudation of H and reductants at a lower Fe concentration than the Fe-efficient Hawkeye (HA), A2, and Bragg, and the Fe-inefficient Pride B216 (Pride), Anoka, and T203 soybean cultivars. The objective of this paper was to assess how soybean response to Fe-deficiency stress affected the general nutrition of the plant. Response to Fe-deficiency stress (H ion and reductant extrusion) was not a good index of total Fe taken up by the plant at higher levels of Fe. For example, as the Fe concentration in solution increased, Bragg took up much more Fe and Mn into both tops and roots than did the other cultivars tested. Pride behaved very much like Bragg and if grown where the supply of Mn is plentiful may develop Mn-toxicity symptoms. With the addition of Fe, both Cu and Zn concentration decreased in tops and roots of all cultivars. Under these same conditions, Ca, K, and P concentrations in top leaves were about the same in all cultivars tested. These data show that Fe-efficiency relates to the ability of the plant to make Fe available under Fe-deficiency stress conditions, and not to the ultimate Fe concentration in the plant material when adequate Fe is supplied or made available.

A7, a new soybean [Glvcine max (L.) Merr.], developed through plant breeding is considered to be more Fe-efficient than cultivars currently available. The objective of this investigation was to determine if recognized factors in the Fe-stress response mechanism may have been altered in A7 soybean to make it more Fe-efficient than the A2, Hawkeye (HA) and Bragg (Fe-efficlent) and the Pride B216 (Pride), T203, and Anoka cultivars (Fe-inef-ficient). The release of hydrogen ions and 'reductants' by the roots were the two parameters of the Fe-stress response studied in this investigation. The effect of plant number per liter of solution was also considered by using 20 and 28 plants per 14 liters of nutrient solution. Compared to A2, HA, Bragg, Pride, Anoka and T203 soybean cultivars, A7 released more hydrogen ions and 'reductant' from its roots in the zero Fe treatment and also maintained higher Fe and chlorophyll concentrations. This could explain why A7 soybean grows better than the other soybeans on calcareous soils where Fe availability limits plant growth. The other cultivars responded to Fe-stress best when a small amount of Fe was present in the nutrient solution. Greater Fe-stress response was evident with 28 plants/14 liters than 20 plants/14 liters of nutrient solution. Successful development of the Fe-efficient soybean should serve as an example for future plant breeding of other Fe-efficient plant species.

The influence of Co on Fe uptake and the Fe-stress response mechanism of tomatoes (Lycopersicon esculentum Mill.) and soybeans [Glycine max (L.) Merr.] was studied. Iron-efficient and -inefficient plants (T3238 fer+ and T3238 fer tomatoes and A7 and T203 soybeans, respectively) were grown in nutrient solutions for seven and nine days at varying Fe and Co levels (0, 0; 1.0, 0; 1.0, 0.3; 1.0, 0.6; 1.0, 1.2; 1.0, 2.4; and 0, 1.2 mg liter-1 Fe and Co, respectively). Cobalt significantly (p≤0.05) decreased chlorophyll and foliar Fe and increased foliar and root Co in all cultivars. Cobalt effects on root Fe varied among cultivars. The Fe-inefficient cultivars were most susceptible to chlorosis in the presence of Co, yet apparently exhibited true Fe deficiency. The Fe-efficient cultivars appeared to exhibit a combination of Fe deficiency and Co toxicity. Chlorophyll formation was generally limited when foliar Fe was below 50 ug Fe g dry weight regardless of Co treatment. Reductant and proton excretion from roots of efficient cultivars apparently did not occur at Co levels where Fe uptake was limiting chlorophyll formation. However, the Fe-efficient cultivars appeared to remain efficient at low Co levels even though the outward measurable indicators (pH and excreted reductant) were not evident. The Fe-stress response mechanism was not observed in Fe-inefficient cultivars regardless of Co level.