Paclobutrazol-induced Drought Tolerance in Containerized English and Evergreen Oak

Glynn C. Percival; Ali Mohammed Salim AlBalushi

doi:10.48044/jauf.2007.046

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Figure 1.
Time course recovery of leaf chlorophyll content (SPAD values) of evergreen oak (Quercus robur L.) placed outdoors after a 21-day drought period. Paclobutrazol (PBZ)-treated plants mean of ten trees, five leaves per tree. Controls, values mean of mean of two trees, five leaves per tree. ▼ = Control; ▲ = 2 mL PBZ foliar spray; ● = 4 mL PBZ foliar spray; ➕ = 5 mL PBZ root drench; ◆ = 10 mL PBZ root drench.
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Figure 2.
Time course recovery of leaf chlorophyll content (SPAD values) of evergreen oak (Quercus ilex L.) placed outdoors after a 21-day drought period. Two milliliters paclobutrazol (PBZ) foliar spray and 5 mL PBZ root drench-treated plant values mean of eight trees, five leaves per tree. Four milliliters PBZ foliar spray and 10 mL PBZ root drench-treated plant values mean of six trees, five leaves per tree. Controls, values mean of mean of four trees, five leaves per tree. ▼ = Control; ▲ = 2 mL PBZ foliar spray; ● = 4 mL PBZ foliar spray; ➕ = 5 mL PBZ root drench; ◆ = 10 mL PBZ root drench.

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Table 1.

Basal (nonstressed) alterations to plant physiology of English oak (Quercus robur L.) at week 2 after paclobutrazol (PBZ) application.^{^z^y}

Parameter	Control	2 mL (0.06 fl oz) PBZ foliar spray	4 mL (0.12 fl oz) PBZ foliar spray	5 mL (0.15 fl oz) PBZ root drench	10 mL (0.3 fl oz) PBZ root drench	Percent change by PBZ
Membrane integrity	2.23	1.79^*	1.89^*	1.70^*	1.67^*	−17.9--33.5
PI	5.81	6.89^*	5.99^ns	7.00^*	6.17^*	+3.3–17.0
Pn	4.87	5.11^*	5.02^ns	5.15^*	5.00^ns	+2.6–5.4
Carotenoids (lutein: β-carotene:neoxanthin:α-carotene)	4.13 (58:17:21:4)	5.28^* (59:16:22:3)	4.40^* (61:15:22:2)	5.63^* (56:19:20:5)	4.48^* (60:17:20:3)	+14.9–21.8
Xanthophylls (zeaxanthin:antheraxanthin:violaxanthin)	3.18 (45:17:38)	3.47^ns (43:18:39)	3.45^ns (46:15:39)	4.50^* (42:18:40)	4.07^* (44:18:38)	+15.5–23.3
Total carotenoids (x + c)	7.31	9.11^*	7.85^*	10.13^*	8.55^*	+17.2–22.3
Proline	117.1	140.4^*	139.0^*	145.0^*	154.3^*	+15.7–24.1
SOD	213.4	245.4^*	222.7^ns	239.7^*	251.4^*	+4.2–15.1
Catalase	845.6	1000.2^*	934.6^*	1228.9^*	1177.8^*	+9.5–31.2
Leaf necrosis	0.1	0.4^*	0.0^ns	0.0^ns	0.0^ns	0-+75
Chlorophyll a/b	2.97	3.01^ns	3.00^ns	2.89^ns	3.05^ns	−2.7-+2.6
Total chlorophylls	82.1	101.3^*	93.5^*	112.5^*	98.3^*	+12.1–27.0

↵^zTrees were placed under glasshouse conditions (22°C ± 2°C [71.6°F ± 35.6°F], 16 hr light/8 hr dark photoperiod and minimum 250 μmol/m⁻²/s⁻¹ photosynthetically active radiation at the tree crown).
↵^yMembrane integrity, PI, chlorophylls, carotenoids, xanthophylls, leaf proline, SOD, catalase, and leaf necrosis values mean of ten trees. Membrane integrity (percent electrolyte leakage), leaf chlorophylls, carotenoids, and xanthophylls content μg/g fresh leaf weight), leaf proline μg/g dry leaf weight), SOD (units g fresh leaf weight), catalase μmol/min⁻¹ g fresh leaf weight).
↵*Significantly different from controls according to least significant difference at P < 0.05; ^ns = not significantly different from control value.
PI = photosynthetic efficiency; Pn = light-induced CO2 fixation; SOD = superoxide dismutase.

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Table 2.

Basal (nonstressed) alterations to plant physiology of evergreen oak (Quercus ilex L.) at week 2 after paclobutrazol (PBZ) application.^{^z^y}

Parameter	Control	2 mL (0.06 fl oz) PBZ foliar spray	4 mL (0.12 fl oz) PBZ foliar spray	5 mL (0.15 fl oz) PBZ root drench	10 mL (0.3 fl oz) PBZ root drench	Percent change by PBZ
Membrane integrity	2.73	1.99*	1.80*	2.33*	2.17*	−14.6–34.1
PI	6.67	7.54*	7.23*	6.88^ns	7.38*	+3.0–11.5
Pn	4.33	4.75^ns	5.27*	4.81^ns	4.49^ns	+3.6–17.8
Carotenoids (lutein: β-carotene:neoxanthin:α-carotene)	4.97 (60:16:21:3)	6.52* (62:14:22:2)	7.23* (59:16:21:4)	7.35* (60:18:20:2)	7.08* (57:19:21:3)	+19.9–24.9
Xanthophylls (zeaxanthin:antheraxanthin:violaxanthin)	3.43 (44:17:39)	4.08* (40:17:43)	4.09* (44:19:37)	4.53* (44:17:39)	4.04* (41:19:40)	+13.2–16.3
Total carotenoids (x + c)	8.41	10.60*	11.32*	11.88*	11.13*	+18.6–22.4
Proline	137.4	165.7*	166.7*	172.1*	159.3^ns	+13.7–20.2
SOD	228.5	266.7*	248.9*	271.5*	302.8*	+8.2–24.5
Catalase	901.5	1243.4*	1338.9*	1435.6*	1269.0*	+27.5–37.2
Leaf necrosis	0.0	0.0^ns	0.0^ns	0.0^ns	0.0^ns	0
Chlorophyll a/b	3.34	3.45^ns	3.32^ns	3.23^ns	3.15^ns	−5.6-+3.2
Total chlorophylls	94.5	117.8*	123.1*	132.5*	126.5*	+19.8–28.6

↵^zTrees were placed under glasshouse conditions (22°C ± 2°C [71.6°F ± 35.6°F], 16 hr light/8 hr dark photoperiod and minimum 250 μmol/m⁻²/s⁻¹ photosynthetically active radiation at the tree crown).
↵^yMembrane integrity, PI, chlorophylls, carotenoids, xanthophylls, leaf proline, SOD, catalase, and leaf necrosis values mean of ten trees. Membrane integrity (percent electrolyte leakage), leaf chlorophylls, carotenoids, and xanthophylls content μg/g fresh leaf weight), leaf proline μg/g dry leaf weight), SOD (units g fresh leaf weight), catalase μmol/min⁻¹ g fresh leaf weight).
*Significantly different from controls according to least significant difference at P < 0.05; ^ns = not significantly different from control value.
PI = photosynthetic efficiency; Pn = light-induced CO2 fixation; SOD = superoxide dismutase.

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Table 3.

The effects of 21 days of drought on chlorophyll fluorescence (PI), photosynthetic CO2 fixation (Pn), leaf chlorophyll content, and necrosis of containerized English oak (Quercus robur L.).^{^z^y}

	PI	Pn	Chlorophyll content	Leaf necrosis	Membrane integrity	Survival (%)
Control	0.18	1.87	30.9	4.1	27.2	20
2 mL (0.06 fl oz) PBZ foliar spray	1.15*	3.38*	38.9*	1.8*	9.8*	100*
4 mL (0.12 fl oz) PBZ foliar spray	2.02*	3.42*	41.1*	2.1*	8.9*	100*
5 mL (0.15 fl oz) PBZ root drench	1.68*	3.52*	48.3*	1.9*	13.2*	100*
10 mL (0.3 fl oz) PBZ root drench	2.41*	3.58*	42.2*	2.0*	9.5*	100*

↵^zMeasurements were made immediately at the cessation of the drought treatment when trees were placed under glasshouse conditions (22°C ± 2°C [71.6°F ± 35.6°F], 16 hr light/8 hr dark photoperiod and minimum 250 μmol/m⁻²/s⁻¹ photosynthetically active radiation at the tree crown.
↵^yPBZ-treated plants: PI and leaf chlorophyll content, values mean of ten trees, five leaves per tree. Pn and electrolyte leakage values mean of ten trees, two leaves per tree. Leaf necrosis values mean of ten trees. Controls: PI and leaf chlorophyll content, values mean of two trees, five leaves per tree. Pn and electrolyte leakage values mean of two trees, two leaves per tree. Leaf necrosis values mean of two trees.
*Significantly different from controls according to least significant difference at P < 0.05; ^ns = not significantly different from control value.
PBZ = paclobutrazol.

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Table 4.

The effects of 21 days of drought on chlorophyll fluorescence (PI), photosynthetic CO2 fixation (Pn), leaf chlorophyll content, and necrosis of containerized evergreen oak (Quercus ilex L.).^{^z^y}

	PI	Pn	Chlorophyll content	Leaf necrosis	Membrane integrity	Survival (%)
Control	1.70	1.59	50.6	3.8	25.4	40
2 mL (0.06 fl oz) PBZ foliar spray	2.27^ns	2.83*	95.8*	2.7^ns	18.6^ns	80*
4 mL (0.12 fl oz) PBZ foliar spray	2.57^ns	1.98^ns	61.0^ns	2.8^ns	17.4^ns	60^ns
5 mL (0.15 fl oz) PBZ root drench	2.42^ns	2.07^ns	68.7^ns	3.0^ns	16.0^ns	80*
10 mL (0.3 fl oz) PBZ root drench	3.34*	1.78^ns	84.3*	2.4^ns	12.3*	60^ns

↵^zMeasurements were made immediately at the cessation of the drought treatment when trees were placed under glasshouse conditions (22°C ± 2°C [71.6°F ± 35.6°F], 16 hr light/8 hr dark photoperiod and minimum 250 μmol/m⁻²/s⁻¹ photosynthetically active radiation at the tree crown).
↵^yTwo milliliters PBZ foliar spray and 5 mL (0.15 fl oz) PBZ root drench-treated plants: PI and leaf chlorophyll content, values mean of eight trees, five leaves per tree. Pn and electrolyte leakage values mean of eight trees, two leaves per tree. Leaf necrosis values mean of ten trees. Four milliliters PBZ foliar spray and 10 mL (0.3 fl oz) PBZ root drench-treated plants: PI and leaf chlorophyll content, values mean of six trees, five leaves per tree. Pn and electrolyte leakage values mean of six trees, two leaves per tree. Leaf necrosis values mean of ten trees. Controls: PI and leaf chlorophyll content, values mean of four trees, five leaves per tree. Pn and electrolyte leakage values mean of four trees, two leaves per tree.
*Significantly different from controls according to least significant difference at P < 0.05; ^ns = not significantly different from control value.
PBZ = paclobutrazol.

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Table 5.

Paclobutrazol enhanced recovery of leaf PI, necrosis, and chlorophyll content of containerized English oak (Quercus robur L.) placed outdoors with time (9 weeks) based on quadratic regression analysis after the cessation of 3 weeks of drought.^{^z}

	PI		Leaf necrosis		Chlorophyll content		Electrolyte leakage (%)
Treatment	Regression: y = a + bT + cT²	_r2	Regression: y = a + bT + ct²	_r2	Regression: y = a + bT + cT²	_r2	Regression: y = a + bT + cT²	_r2
Control	y = −2.39 + 2.52T − 0.21T²	0.90	y = 4.06 + 0.05T − 0.04T²	0.89	y = 22.3 + 9.98T − 1.07T²	0.95	y = 28.2 − 1.56T − 0.21T²	0.92
2 mL (0.06 fl oz) PBZ foliar spray	y = −1.58 + 2.55 − 0.19T²	0.83	y = 1.97 − 0.20T + 0.01T²	0.91	y = 34.8 + 2.48T + 0.22T²	0.98	y = 13.0 −3.32T + 0.25T²	0.85
4 mL (0.12 fl oz) PBZ foliar spray	y = 1.36 + 0.70T + 0.02T²	0.87	y = 2.47 − 0.34T + 0.02T²	0.73	y = 28.4 + 11.47T − 0.38T²	0.93	y = 8.94 − 0.04T − 0.13T²	0.83
5 mL (0.15 fl oz) PBZ root drench	y = 0.62 + 1.30T − 0.06T²	0.47	y = 2.15 − 0.20T + 0.00T²	0.90	y = 51.2 − 4.48T + 1.83T²	0.77	y = 15.3 − 2.07T − 0.00T²	0.96
10 mL (0.3 fl oz) PBZ root drench	y = 0.17 + 2.66T − 0.28T²	0.77	y = 2.33 − 0.25T + 0.01T²	0.86	y = 34.8 + 8.32T − 0.21T²	0.81	y = 9.48 − 0.28T − 0.19T²	0.93

↵^zPBZ-treated plants: PI and leaf chlorophyll content, values mean of ten trees, five leaves per tree. Electrolyte leakage values mean of ten trees, two leaves per tree. Leaf necrosis values mean of ten trees. Controls: PI and leaf chlorophyll content, values mean of two trees, five leaves per tree. Pn and electrolyte leakage values mean of two trees, two leaves per tree. Leaf necrosis values mean of two trees.
Y = leaf PI, necrosis, chlorophyll content, and electrolyte leakage value; a = leaf PI, necrosis, chlorophyll content, and electrolyte leakage of control value (calculated intercept); b = rate of PI, necrosis, chlorophyll content and electrolyte leakage with time (T); c = rate of change of leaf PI, necrosis, chlorophyll content, and electrolyte leakage.
PBZ = paclobutrazol; PI = chlorophyll fluorescence.

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Table 6.

Paclobutrazol enhanced recovery of leaf PI, necrosis, and chlorophyll content of containerized evergreen oak (Quercus ilex L.) placed outdoors with time (9 weeks) based on quadratic regression analysis after the cessation of 3 weeks of drought.^{^z}

	PI		Leaf necrosis		Chlorophyll content		Electrolyte leakage (%)
Treatment	Regression: y = a + bT + cT²	r²	Regression: y = a + bT + cT²	r²	Regression: y = a + bT + cT²	r²	Regression: y = a + bT + cT²	r²
Control	y = 0.88 + 0.309T + 0.07T²	0.93	y = 4.06 − 0.14T − 0.021²	0.92	y = 46.7 + 3.60T + 0.20T²	0.90	y = 31.5 − 5.81T + 0.45T²	0.90
2 mL (0.06 fl oz) PBZ foliar spray	y = 0.16 + 1.99T − 0.13T²	0.94	y = 2.62 − 0.01T − 0.01T²	0.70	y = 88.1 + 5.97T − 0.52T²	0.88	y = 20.1 − 1.66T − 0.14T²	0.95
4 mL (0.12 fl oz) PBZ foliar spray	y = −0.20 + 3.04T − 0.30T²	0.90	y = 3.29 − 0.50T + 0.04T²	0.96	y = 55.2 + 6.44T + 0.64T²	0.89	y = 20.7 − 2.57T + 0.09T²	0.87
5 mL (0.15 fl oz) PBZ root drench	y = 1.33 + 0.807T + 0.02T²	0.97	y = 3.01 − 0.10T − 0.01T²	0.96	y = 61.3 + 7.53T − 0.01T²	0.71	y = 16.1 − 0.17T − 0.32T²	0.82
10 mL (0.3 fl oz) PBZ root drench	y = 1.57 + 1.79T − 0.14T²	0.95	y = 2.54 + 0.20T − 0.00T²	0.93	y = 82.0 + 0.52T + 0.83T²	0.88	y = 10.9 + 1.36T − 0.40T²	0.99

↵^zTwo milliliters PBZ foliar spray and 5 mL (0.15 fl oz) PBZ root drench-treated plants: PI and leaf chlorophyll content, values mean of eight trees, five leaves per tree. Pn and electrolyte leakage values mean of eight trees, two leaves per tree. Leaf necrosis values mean of eight trees. Four milliliters PBZ foliar spray and 10 mL (0.3 fl oz) PBZ root drench-treated plants: PI and leaf chlorophyll content, values mean of six trees, five leaves per tree. Pn and electrolyte leakage values mean of six trees, two leaves per tree. Leaf necrosis values mean of six trees. Controls: PI and leaf chlorophyll content, values mean of four trees, five leaves per tree. Pn and electrolyte leakage values mean of four trees, two leaves per tree. Leaf necrosis values mean of four trees.
y = leaf PI, necrosis, chlorophyll content, and electrolyte leakage value; a = leaf PI, necrosis, chlorophyll content, and electrolyte leakage of control value (calculated intercept); b = rate of PI, necrosis, chlorophyll content, and electrolyte leakage with time (T); c = rate of change of leaf PI, necrosis, chlorophyll content, and electrolyte leakage.
PBZ = paclobutrazol; PI = chlorophyll fluorescence; Pn = photosynthetic CO2 fixation.

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Table 7.

Influence of PBZ on height and mean leaf size of containerized English (Quercus robur L.) and evergreen oak (Quercus ilex L.) placed outdoors over a 9-week period after the cessation of a 3-week drought period.^{^z}

Treatment	Evergreen Oak		English Oak
Treatment	Height (m)	Mean leaf size (cm²)	Height (m)	Mean leaf size (cm²)
Control	1.05	8.9	1.15	49.3
2 mL (0.06 fl oz) PBZ foliar spray	0.96^ns	8.4^ns	0.99^ns	43.1^ns
4 mL (0.12 fl oz) PBZ foliar spray	0.83^ns	6.0*	0.86*	32.2*
5 mL (0.15 fl oz) PBZ root drench	0.79*	4.5*	0.80*	28.5*
10 mL (0.3 fl oz) PBZ root drench	0.68*	4.3*	0.76*	26.7*
LSD	0.245	2.759	0.276	15.26

↵^zEnglish oak PBZ-treated plants: all values mean of ten trees. English oak control: all values mean of two trees.
Evergreen oak 2 mL (0.06 fl oz) PBZ foliar spray and 5 mL (0.15 fl oz) PBZ root drench-treated plants mean of eight trees. Four milliliters PBZ foliar spray and 10 mL (0.3 fl oz) PBZ root drench-treated plants mean of six trees.
Controls mean of four trees.
*Significantly different from controls according to least significant difference (LSD) at P < 0.05; ^ns = not significantly different from control value.
PBZ = paclobutrazol.